[clang] [OpenMP] Add support for Solaris/x86_64 (PR #70593)

[Shilei Tian via cfe-commits]

shiltian wrote:

> > I'm not familiar with Solaris but does it need dedicated implementation of the function invocation written in ASM?
> 
> Can you point out what you're referring to? Looking at the patches for adding support for OpenBSD and other OS's I don't see any ASM additions.

I was thinking about `openmp/runtime/src/z_Linux_asm.S` but it looks like we don't need extra stuff there.

https://github.com/llvm/llvm-project/pull/70593