Some improvements for MinGW and LLVM build on Windows

[alvinhochun]

This PR aims to improve the MinGW developer experience, especially for llvm-mingw on Windows:

• Detect llvm-mingw - this toolchain provides GCC-like wrappers (e.g. x86_64-w64-mingw-gcc.exe) that helps using the toolchain as a drop-in replacement of GCC, but because the Godot build has some special logic for LLVM based on the use_llvm option, it will be better if the build script detects this situation and automatically set use_llvm=True.
• Enable Clang colour output if supported on terminal (self explanatory)
• Use thin archives - full archive files take a lot of space (1.3 GB total) compared to thin archives (57 MB total). (This is with llvm-mingw doing an editor dev build, other builds may vary.)
  • Something to note is that the --thin flag is only supported for llvm-ar since LLVM 14 from 2022 (binutils ar has had it for ages). Do we need to support older LLVM versions? Adding a check for this would be annoying though.
• Print compiler warnings when building on Windows
• ...and some minor changes.

[Calinou]

Do we need to support older LLVM versions?

I'd say it's fine to require a recent (still 3 2 years old) LLVM version on Windows, as it's easy to install a recent version there (unlike Linux distributions where this can require third-party repositories).

[alvinhochun]

Oh sorry, LLVM 14 was actually early 2022. I mis-wrote.

Regardless, trying to use a distro build of LLVM together with a distro build of mingw-w64 runtime to cross-compile is not quite straightforward, so I honestly would not expect many people (if any at all) to do it with Godot. (Not to mention that GCC is still the usual compiler people use to target MinGW.)

[Calinou]

Tested locally, it works as expected (Windows 11 23H2, LLVM 17.0.6 from https://github.com/mstorsjo/llvm-mingw/releases/tag/20231128). The resulting binary runs correctly.

[bruvzg]

Not sure how this is related to PR and why it's removed., nothing seems to fix the mentioned issue, so it's likely still relevant.

[alvinhochun]

Hmm, let me remove this commit from the PR. I will check again some time and handle it in another PR.

[akien-mga]

Thanks!