[llvm] Set Support system_libs if WIN32, not just MSVC or MINGW (PR #95505)

[Jeremy Day via llvm-commits]

z2oh wrote:

Ah I didn't know that! I assumed it took the commit's message. I've removed the extra comments from the first post, and pasted them below for posterity:
> I added the reference to RtlGetLastNtStatus in https://github.com/llvm/llvm-project/pull/90655.
> 
> I tried building with clang++ without this change, saw the undefined symbol error, then tried building again with if( WIN32 ) here and was able to build successfully.
> 
> Thanks @mstorsjo for suggesting this straightforward fix.

https://github.com/llvm/llvm-project/pull/95505