SCons: Add proper MinGW support to D3D12 deps install script

[akien-mga]

I'm not super happy about the change in platform/windows/detect.py to figure out whether to modify the env["mesa_libs"] path to add a -mingw suffix...

Open to suggestions to make this less hacky, especially having to pass the detected d3d12 deps path as an option, because we can't easily pass info otherwise from get_opts to the env or configure_mingw (global doesn't seem to work).

Might also work on macOS to cross-compile, worth testing.

[bruvzg]

Maybe we should update Mesa to the current release - 23.3.4 (GitHub mirror seems to be outdated, and active repo is https://gitlab.freedesktop.org/mesa/mesa/), and make a single release with both MinGW and MSVC files.

[akien-mga]

That would be nice yeah, it should simplify the script so we don't have to make assumptions, if we can just rely on mesa_path being either custom or the target of the install script for both MSVC and MinGW.

[akien-mga]

Redid this PR now that https://github.com/godotengine/godot-nir-static/ has both MSVC and MinGW support in the same tarball.

There's no more command line options, but instead we rely on whether we find gendef and dlltool to see if the .a files should be generated for PIX. Needs to be checked if that doesn't break the script on Windows both when MinGW is installed and not installed/in PATH.

[Calinou]

Tested locally on Windows 11 with llvm-mingw 20231128, it works as expected. The resulting D3D12 build can be run just fine.

Note that if your llvm-mingw version is older (I had a version from 2022 lying around), I got the following output with it (but the .a generation was still successful):

[3/4] WinPixEventRuntime
Downloading WinPixEventRuntime 1.0.231030001 ...
Extracting WinPixEventRuntime 1.0.231030001 to C:\Users\Hugo\AppData\Local\Godot\build_deps\pix ...
Converting WinPixEventRuntime.dll for MinGW.
 * [./bin/x64/WinPixEventRuntime.dll] Found PE+ image
ignoring unknown argument: --no-leading-underscore
 * [./bin/ARM64/WinPixEventRuntime.dll] Found PE+ image
ignoring unknown argument: --no-leading-underscore
WinPixEventRuntime 1.0.231030001 installed successfully.

The script still works successfully if I rename my llvm-mingw folder so it's no longer in PATH.