SCons: Refactor Linux linker options with `linker=<bfd|gold|lld|mold>`

The new option is `linker` and lets the user specify the argument to
the`-fuse_ld=` linker flag directly. The supported options are:

- `default`: No change, typically uses GNU ld (bfd) unless the user or
  distro picked a different default `/usr/bin/ld`.
- `bfd`: GNU ld from binutils
- `gold`: GNU gold from binutils
- `lld`: lld from LLVM
- `mold`: mold, an extremely fast modern linker, not (yet) intended for
  use in production but great for development speed. Provided by distro
  `mold` package or needs to be compiled from source and installed to
  `/usr` otherwise.

Removes the `use_lld=yes` option, and make lld actually usable with GCC
too.

Not all the above are compatible or recommend for LTO, we recommend
using GNU ld with GCC LTO, or lld with LLVM ThinLTO.

0 files changed, 0 insertions, 0 deletions