Fix warning about functions defined but not used [-Wunused-function]

Fixes the following GCC 5 warnings:
```
core/io/zip_io.h:128:26: warning: 'zlib_filefunc_def zipio_create_io_from_file(FileAccess**)' defined but not used [-Wunused-function]
core/script_debugger_remote.cpp:110:17: warning: 'ObjectID safe_get_instance_id(const Variant&)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:103:12: warning: 'int _socket_create(IP::Type&, int, int)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:45:15: warning: 'size_t _set_sockaddr(sockaddr_storage*, const IP_Address&, int, IP::Type)' defined but not used [-Wunused-function]
drivers/unix/socket_helpers.h:76:15: warning: 'size_t _set_listen_sockaddr(sockaddr_storage*, int, IP::Type, IP_Address)' defined but not used [-Wunused-function]
editor/editor_fonts.cpp:40:24: warning: 'Ref<BitmapFont> make_font(int, int, int, int, const int*, const Ref<Texture>&)' defined but not used [-Wunused-function]
editor/editor_themes.cpp:85:26: warning: 'Ref<StyleBoxFlat> change_border_color(Ref<StyleBoxFlat>, Color)' defined but not used [-Wunused-function]
editor/import/editor_import_collada.cpp:493:13: warning: 'void _generate_normals(const PoolVector<int>&, const PoolVector<Vector3>&, PoolVector<Vector3>&)' defined but not used [-Wunused-function]
editor/import/editor_import_collada.cpp:524:13: warning: 'void _generate_tangents_and_binormals(const PoolVector<int>&, const PoolVector<Vector3>&, const PoolVector<Vector3>&, const PoolVector<Vector3>&, PoolVector<float>&)' defined but not used [-Wunused-function]
editor/pvrtc_compress.cpp:118:13: warning: 'void _compress_etc(Image*)' defined but not used [-Wunused-function]
modules/etc/image_etc.cpp:89:13: warning: 'void _decompress_etc1(Image*)' defined but not used [-Wunused-function]
modules/etc/image_etc.cpp:93:13: warning: 'void _decompress_etc2(Image*)' defined but not used [-Wunused-function]
modules/gdscript/editor/gdscript_highlighter.cpp:46:13: warning: 'bool _is_whitespace(CharType)' defined but not used [-Wunused-function]
scene/2d/cpu_particles_2d.cpp:510:14: warning: 'float rand_from_seed_m1_p1(uint32_t&)' defined but not used [-Wunused-function]
scene/3d/cpu_particles.cpp:474:14: warning: 'float rand_from_seed_m1_p1(uint32_t&)' defined but not used [-Wunused-function]
scene/resources/default_theme/default_theme.cpp:123:20: warning: 'Ref<Shader> make_shader(const char*, const char*, const char*)' defined but not used [-Wunused-function]
scene/resources/default_theme/default_theme.cpp:130:24: warning: 'Ref<BitmapFont> make_font(int, int, int, int, const int*, const Ref<Texture>&)' defined but not used [-Wunused-function]
```

Had to split `core/io/zip_io.h` into header and .cpp file without 'static' keyword.

Not fixed yet (static definition in header used in some files but not all):
```
modules/websocket/lws_helper.h:111:13: warning: 'void _lws_make_protocols(void*, int (*)(lws*, lws_callback_reasons, void*, void*, size_t), PoolVector<String>, _LWSRef**)' defined but not used [-Wunused-function]
```

Also fixed a couple other warnings missed in previous commits.

2 files changed, 150 insertions, 99 deletions

diff --git a/core/io/zip_io.cpp b/core/io/zip_io.cpp
new file mode 100644
index 0000000000..b7f841b66f
--- /dev/null
+++ b/core/io/zip_io.cpp
@@ -0,0 +1,137 @@
+/*************************************************************************/
+/*  zip_io.cpp                                                           */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2018 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2018 Godot Engine contributors (cf. AUTHORS.md)    */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "zip_io.h"
+
+#include "core/os/copymem.h"
+
+void *zipio_open(void *data, const char *p_fname, int mode) {
+
+	FileAccess *&f = *(FileAccess **)data;
+
+	String fname;
+	fname.parse_utf8(p_fname);
+
+	if (mode & ZLIB_FILEFUNC_MODE_WRITE) {
+		f = FileAccess::open(fname, FileAccess::WRITE);
+	} else {
+
+		f = FileAccess::open(fname, FileAccess::READ);
+	}
+
+	if (!f)
+		return NULL;
+
+	return data;
+}
+
+uLong zipio_read(void *data, void *fdata, void *buf, uLong size) {
+
+	FileAccess *f = *(FileAccess **)data;
+	return f->get_buffer((uint8_t *)buf, size);
+}
+
+uLong zipio_write(voidpf opaque, voidpf stream, const void *buf, uLong size) {
+
+	FileAccess *f = *(FileAccess **)opaque;
+	f->store_buffer((uint8_t *)buf, size);
+	return size;
+}
+
+long zipio_tell(voidpf opaque, voidpf stream) {
+
+	FileAccess *f = *(FileAccess **)opaque;
+	return f->get_position();
+}
+
+long zipio_seek(voidpf opaque, voidpf stream, uLong offset, int origin) {
+
+	FileAccess *f = *(FileAccess **)opaque;
+
+	int pos = offset;
+	switch (origin) {
+
+		case ZLIB_FILEFUNC_SEEK_CUR:
+			pos = f->get_position() + offset;
+			break;
+		case ZLIB_FILEFUNC_SEEK_END:
+			pos = f->get_len() + offset;
+			break;
+		default:
+			break;
+	};
+
+	f->seek(pos);
+	return 0;
+}
+
+int zipio_close(voidpf opaque, voidpf stream) {
+
+	FileAccess *&f = *(FileAccess **)opaque;
+	if (f) {
+		f->close();
+		f = NULL;
+	}
+	return 0;
+}
+
+int zipio_testerror(voidpf opaque, voidpf stream) {
+
+	FileAccess *f = *(FileAccess **)opaque;
+	return (f && f->get_error() != OK) ? 1 : 0;
+}
+
+voidpf zipio_alloc(voidpf opaque, uInt items, uInt size) {
+
+	voidpf ptr = memalloc(items * size);
+	zeromem(ptr, items * size);
+	return ptr;
+}
+
+void zipio_free(voidpf opaque, voidpf address) {
+
+	memfree(address);
+}
+
+zlib_filefunc_def zipio_create_io_from_file(FileAccess **p_file) {
+
+	zlib_filefunc_def io;
+	io.opaque = p_file;
+	io.zopen_file = zipio_open;
+	io.zread_file = zipio_read;
+	io.zwrite_file = zipio_write;
+	io.ztell_file = zipio_tell;
+	io.zseek_file = zipio_seek;
+	io.zclose_file = zipio_close;
+	io.zerror_file = zipio_testerror;
+	io.alloc_mem = zipio_alloc;
+	io.free_mem = zipio_free;
+	return io;
+}
diff --git a/core/io/zip_io.h b/core/io/zip_io.h
index c3314a8990..bba7d67332 100644
--- a/core/io/zip_io.h
+++ b/core/io/zip_io.h
@@ -31,114 +31,28 @@
 #ifndef ZIP_IO_H
 #define ZIP_IO_H
 
-#include "core/os/copymem.h"
 #include "core/os/file_access.h"
 
+// Not direclty used in this header, but assumed available in downstream users
+// like platform/*/export/export.cpp. Could be fixed, but probably better to have
+// thirdparty includes in as little headers as possible.
 #include "thirdparty/minizip/unzip.h"
 #include "thirdparty/minizip/zip.h"
 
-static void *zipio_open(void *data, const char *p_fname, int mode) {
+void *zipio_open(void *data, const char *p_fname, int mode);
+uLong zipio_read(void *data, void *fdata, void *buf, uLong size);
+uLong zipio_write(voidpf opaque, voidpf stream, const void *buf, uLong size);
 
-	FileAccess *&f = *(FileAccess **)data;
+long zipio_tell(voidpf opaque, voidpf stream);
+long zipio_seek(voidpf opaque, voidpf stream, uLong offset, int origin);
 
-	String fname;
-	fname.parse_utf8(p_fname);
+int zipio_close(voidpf opaque, voidpf stream);
 
-	if (mode & ZLIB_FILEFUNC_MODE_WRITE) {
-		f = FileAccess::open(fname, FileAccess::WRITE);
-	} else {
+int zipio_testerror(voidpf opaque, voidpf stream);
 
-		f = FileAccess::open(fname, FileAccess::READ);
-	}
+voidpf zipio_alloc(voidpf opaque, uInt items, uInt size);
+void zipio_free(voidpf opaque, voidpf address);
 
-	if (!f)
-		return NULL;
-
-	return data;
-};
-
-static uLong zipio_read(void *data, void *fdata, void *buf, uLong size) {
-
-	FileAccess *f = *(FileAccess **)data;
-	return f->get_buffer((uint8_t *)buf, size);
-};
-
-static uLong zipio_write(voidpf opaque, voidpf stream, const void *buf, uLong size) {
-
-	FileAccess *f = *(FileAccess **)opaque;
-	f->store_buffer((uint8_t *)buf, size);
-	return size;
-};
-
-static long zipio_tell(voidpf opaque, voidpf stream) {
-
-	FileAccess *f = *(FileAccess **)opaque;
-	return f->get_position();
-};
-
-static long zipio_seek(voidpf opaque, voidpf stream, uLong offset, int origin) {
-
-	FileAccess *f = *(FileAccess **)opaque;
-
-	int pos = offset;
-	switch (origin) {
-
-		case ZLIB_FILEFUNC_SEEK_CUR:
-			pos = f->get_position() + offset;
-			break;
-		case ZLIB_FILEFUNC_SEEK_END:
-			pos = f->get_len() + offset;
-			break;
-		default:
-			break;
-	};
-
-	f->seek(pos);
-	return 0;
-};
-
-static int zipio_close(voidpf opaque, voidpf stream) {
-
-	FileAccess *&f = *(FileAccess **)opaque;
-	if (f) {
-		f->close();
-		f = NULL;
-	}
-	return 0;
-};
-
-static int zipio_testerror(voidpf opaque, voidpf stream) {
-
-	FileAccess *f = *(FileAccess **)opaque;
-	return (f && f->get_error() != OK) ? 1 : 0;
-};
-
-static voidpf zipio_alloc(voidpf opaque, uInt items, uInt size) {
-
-	voidpf ptr = memalloc(items * size);
-	zeromem(ptr, items * size);
-	return ptr;
-}
-
-static void zipio_free(voidpf opaque, voidpf address) {
-
-	memfree(address);
-}
-
-static zlib_filefunc_def zipio_create_io_from_file(FileAccess **p_file) {
-
-	zlib_filefunc_def io;
-	io.opaque = p_file;
-	io.zopen_file = zipio_open;
-	io.zread_file = zipio_read;
-	io.zwrite_file = zipio_write;
-	io.ztell_file = zipio_tell;
-	io.zseek_file = zipio_seek;
-	io.zclose_file = zipio_close;
-	io.zerror_file = zipio_testerror;
-	io.alloc_mem = zipio_alloc;
-	io.free_mem = zipio_free;
-	return io;
-}
+zlib_filefunc_def zipio_create_io_from_file(FileAccess **p_file);
 
 #endif // ZIP_IO_H