17.2.3.500-1

• Updated Mesa3D to 17.2.3.
• Built S3TC with MSYS2 Mingw-w64 GCC 7.2.0.
• Built LLVM 5.0 and Mesa with Visual Studio 2017 v15.4.0.

Deployment utility

• Made easy to swap osmesa variants.
• Check before attempting to create symbolic links. Avoid harmless errors which may be confusing.

Build script

• Drop S3TC build if Mesa master source code is detected. S3TC is now built-in. Texture cache enabling patch is still needed though.
• Python modules updating: use both pip install -U explicitly and pip freeze in a hybrid approach for most optimal behavior.
• Improved PATH cleanning.
• Support building S3TC with MSYS2 Mingw-W64 GCC by default. They fixed their problem with 32-bit binaries when they upgraded to GCC 7.2.0 (Alexpux/MINGW-packages#2271).
• Drop suport for Visual Studio 2015 completely. It survived so long due to Scons 3.0.0 issues.
• Mesa build without git workaround: git_sha1.h was generated in an incorrect location during 64-bit builds.
• Drop Scons 3.0.0 compatibility patch. It landed in Mesa 17.2.3.
• Allow building Mesa without git since Scons 3.0.0 compatibility patch landed in Mesa stable.

Build script documentation

• MSYS2 Mingw-w64 is now the preferred method to build S3TC.
• Visual Studio 2017 is now required to build LLVM and Mesa3D.