Fix warnings for comparison between signed and unsigned integers [-Wsign-compare]

Also turn off -Wsign-compare warnings in the future, we do not consider them important.

Fixes the following GCC 5 warnings:
```
core/node_path.cpp:279:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
core/oa_hash_map.h:169:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
core/oa_hash_map.h:314:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/gles2/shader_gles2.cpp:985:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/gles3/rasterizer_storage_gles3.cpp:1075:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/pulseaudio/audio_driver_pulseaudio.cpp:343:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
editor/editor_plugin.cpp:525:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
editor/editor_properties_array_dict.cpp:747:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
editor/plugins/spatial_editor_plugin.cpp:2078:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
editor/plugins/spatial_editor_plugin.cpp:4096:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
editor/plugins/sprite_editor_plugin.cpp:100:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/cvtt/image_compress_cvtt.cpp:122:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/cvtt/image_compress_cvtt.cpp:134:77: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/cvtt/image_compress_cvtt.cpp:339:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/etc/image_etc.cpp:222:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/gdnative/register_types.cpp:242:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/gdnative/register_types.cpp:258:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/opensimplex/simplex_noise.cpp:200:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/opensimplex/simplex_noise.cpp:222:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
modules/opensimplex/simplex_noise.cpp:246:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/android/export/export.cpp:1085:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/android/export/export.cpp:1489:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/android/export/export.cpp:1623:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/iphone/export/export.cpp:206:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/iphone/export/export.cpp:356:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/iphone/export/export.cpp:406:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
platform/iphone/export/export.cpp:493:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/3d/audio_stream_player_3d.cpp:420:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/resources/audio_stream_sample.cpp:565:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/resources/audio_stream_sample.cpp:571:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio/audio_rb_resampler.cpp:156:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
```

The following warnings were not fixed, as they implied casting for no gain:
```
core/io/packet_peer.cpp:228:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
core/io/resource_format_binary.cpp:109:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/gles2/rasterizer_scene_gles2.cpp:144:57: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/unix/file_access_unix.cpp:249:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/3d/voxel_light_baker.cpp:889:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/3d/voxel_light_baker.cpp:1020:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/3d/voxel_light_baker.cpp:1154:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/3d/voxel_light_baker.cpp:2255:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
scene/resources/bit_mask.cpp:336:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio/audio_stream.cpp:141:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio/audio_stream.cpp:150:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio/audio_stream.cpp:154:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio_server.cpp:86:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
servers/audio_server.cpp:89:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
```

4 files changed, 9 insertions, 9 deletions

diff --git a/modules/cvtt/image_compress_cvtt.cpp b/modules/cvtt/image_compress_cvtt.cpp
index 17af6bff09..425d8db183 100644
--- a/modules/cvtt/image_compress_cvtt.cpp
+++ b/modules/cvtt/image_compress_cvtt.cpp
@@ -118,7 +118,7 @@ static void _digest_row_task(const CVTTCompressionJobParams &p_job_params, const
 			cvtt::Kernels::EncodeBC7(output_blocks, input_blocks_ldr, p_job_params.options);
 		}
 
-		int num_real_blocks = ((w - x_start) + 3) / 4;
+		unsigned int num_real_blocks = ((w - x_start) + 3) / 4;
 		if (num_real_blocks > cvtt::NumParallelBlocks) {
 			num_real_blocks = cvtt::NumParallelBlocks;
 		}
@@ -131,7 +131,7 @@ static void _digest_row_task(const CVTTCompressionJobParams &p_job_params, const
 static void _digest_job_queue(void *p_job_queue) {
 	CVTTCompressionJobQueue *job_queue = static_cast<CVTTCompressionJobQueue *>(p_job_queue);
 
-	for (int next_task = atomic_increment(&job_queue->current_task); next_task <= job_queue->num_tasks; next_task = atomic_increment(&job_queue->current_task)) {
+	for (uint32_t next_task = atomic_increment(&job_queue->current_task); next_task <= job_queue->num_tasks; next_task = atomic_increment(&job_queue->current_task)) {
 		_digest_row_task(job_queue->job_params, job_queue->job_tasks[next_task - 1]);
 	}
 }
@@ -335,7 +335,7 @@ void image_decompress_cvtt(Image *p_image) {
 				uint8_t input_blocks[16 * cvtt::NumParallelBlocks];
 				memset(input_blocks, 0, sizeof(input_blocks));
 
-				int num_real_blocks = ((w - x_start) + 3) / 4;
+				unsigned int num_real_blocks = ((w - x_start) + 3) / 4;
 				if (num_real_blocks > cvtt::NumParallelBlocks) {
 					num_real_blocks = cvtt::NumParallelBlocks;
 				}
diff --git a/modules/etc/image_etc.cpp b/modules/etc/image_etc.cpp
index a534aec11b..fd17c7b81f 100644
--- a/modules/etc/image_etc.cpp
+++ b/modules/etc/image_etc.cpp
@@ -174,7 +174,7 @@ static void _compress_etc(Image *p_img, float p_lossy_quality, bool force_etc1_f
 
 	PoolVector<uint8_t>::Read r = img->get_data().read();
 
-	int target_size = Image::get_image_data_size(imgw, imgh, etc_format, p_img->has_mipmaps());
+	unsigned int target_size = Image::get_image_data_size(imgw, imgh, etc_format, p_img->has_mipmaps());
 	int mmc = 1 + (p_img->has_mipmaps() ? Image::get_image_required_mipmaps(imgw, imgh, etc_format) : 0);
 
 	PoolVector<uint8_t> dst_data;
diff --git a/modules/gdnative/register_types.cpp b/modules/gdnative/register_types.cpp
index 48c0fc8aef..f56778b296 100644
--- a/modules/gdnative/register_types.cpp
+++ b/modules/gdnative/register_types.cpp
@@ -239,7 +239,7 @@ void GDNativeExportPlugin::_export_file(const String &p_path, const String &p_ty
 		String additional_code = "extern void register_dynamic_symbol(char *name, void *address);\n"
 								 "extern void add_ios_init_callback(void (*cb)());\n";
 		String linker_flags = "";
-		for (int i = 0; i < sizeof(expected_symbols) / sizeof(expected_symbols[0]); ++i) {
+		for (unsigned int i = 0; i < sizeof(expected_symbols) / sizeof(expected_symbols[0]); ++i) {
 			String full_name = lib->get_symbol_prefix() + expected_symbols[i].name;
 			String code = declare_pattern.replace("$name", full_name);
 			code = code.replace("$weak", expected_symbols[i].is_required ? "" : " __attribute__((weak))");
@@ -255,7 +255,7 @@ void GDNativeExportPlugin::_export_file(const String &p_path, const String &p_ty
 
 		additional_code += String("void $prefixinit() {\n").replace("$prefix", lib->get_symbol_prefix());
 		String register_pattern = "  if (&$name) register_dynamic_symbol((char *)\"$name\", (void *)$name);\n";
-		for (int i = 0; i < sizeof(expected_symbols) / sizeof(expected_symbols[0]); ++i) {
+		for (unsigned int i = 0; i < sizeof(expected_symbols) / sizeof(expected_symbols[0]); ++i) {
 			String full_name = lib->get_symbol_prefix() + expected_symbols[i].name;
 			additional_code += register_pattern.replace("$name", full_name);
 		}
diff --git a/modules/opensimplex/simplex_noise.cpp b/modules/opensimplex/simplex_noise.cpp
index e489b7f6f0..c99fd7b123 100644
--- a/modules/opensimplex/simplex_noise.cpp
+++ b/modules/opensimplex/simplex_noise.cpp
@@ -196,7 +196,7 @@ float SimplexNoise::get_noise_2d(float x, float y) {
 	float max = 1.0;
 	float sum = _get_octave_noise_2d(0, x, y);
 
-	unsigned int i = 0;
+	int i = 0;
 	while (++i < octaves) {
 		x *= lacunarity;
 		y *= lacunarity;
@@ -218,7 +218,7 @@ float SimplexNoise::get_noise_3d(float x, float y, float z) {
 	float max = 1.0;
 	float sum = _get_octave_noise_3d(0, x, y, z);
 
-	unsigned int i = 0;
+	int i = 0;
 	while (++i < octaves) {
 		x *= lacunarity;
 		y *= lacunarity;
@@ -242,7 +242,7 @@ float SimplexNoise::get_noise_4d(float x, float y, float z, float w) {
 	float max = 1.0;
 	float sum = _get_octave_noise_4d(0, x, y, z, w);
 
-	unsigned int i = 0;
+	int i = 0;
 	while (++i < octaves) {
 		x *= lacunarity;
 		y *= lacunarity;