llvm: update to 20.1.0

[MehdiChinoune]

No description provided.

[MehdiChinoune]

I have pushed only llvm and libc++ so the job won't time-out. I managed to build all other components

About the Rebuilds:

• mingw-w64-arrow requires a simple patch to accept LLVM-20
• mingw-w64-castxml
• mingw-w64-creduce practically unmaintained, fails as usual
• mingw-w64-crystal requires two backports crystal-lang/crystal@1c03dfa3 and crystal-lang/crystal@1fafbb2b
• mingw-w64-cvise requires one backport marxin/cvise@29fc072f
• mingw-w64-ghdl requires a simple patch to accept LLVM-20
• mingw-w64-include-what-you-use requires one backport include-what-you-use/include-what-you-use@e2e42c6b
• mingw-w64-mesa
• mingw-w64-openshadinglanguage rebuild with LLVM-16
• mingw-w64-qt-creator
• mingw-w64-qt6-static
• mingw-w64-qt6-tools
• mingw-w64-spirv-llvm-translator should be built from llvm_release_200 branch, usually they release a version shortly after LLVM final release. Also requires spirv-headers to backport some changes KhronosGroup/SPIRV-Headers@9ca0e67b and KhronosGroup/SPIRV-Headers@2b2e05e0.
• mingw-w64-zig should be built from llvm20 branch which is an open PR LLVM 20 ziglang/zig#22780

I think we could update to LLVM 20.1.0 once It's released.

[n0F4x]

I am trying to compile my project with clang 20, but I ran into some problems.

In file included from C:\dev\msys64\clang64/include/c++/v1/cmath:331:
In file included from C:\dev\msys64\clang64/include/c++/v1/math.h:383:
In file included from C:\dev\msys64\clang64/include/c++/v1/stdlib.h:89:
In file included from C:\dev\msys64\clang64/include/stdlib.h:719:
C:\dev\msys64\clang64/include/malloc.h:138:10: fatal error: 'mm_malloc.h' file not found