might want to check your facts before spouting nonsense. there is, and has been for many, many years. more than one in fact:
https://github.com/mstorsjo/llvm-mingw
https://packages.msys2.org/base/mingw-w64-gcc
https://mirrors.kernel.org/sourceware/cygwin/x86_64/release/...
Personally I use https://github.com/mstorsjo/llvm-mingw's releases directly which does not require MSYS but that's because I recompile all my libraries with specific options - if the MSYS libs as they are built are good for you there's no reason not to use them.
Actually, (upstream) Clang defaults to native TLS instead of emulated TLS. In MSYS2, Clang is overridden to use emulated TLS by deafult to interoperate better with GCC built code and libstdc++ though.
The toolchain I maintain, https://github.com/mstorsjo/llvm-mingw, defaults to native TLS throughout.
Win32 is supported with MSVC just fine.
You can also use MinGW with LLVM (not MinGW with GCC), available at: https://github.com/mstorsjo/llvm-mingw