[clang] [Clang] Don't use crtbegin/crtend when building for musl. (PR #85089)

[Alastair Houghton via cfe-commits]

al45tair wrote:

> The compiler provides crtbegin/crtend files, not musl.

Interesting. Looking at the LLVM repo, it seems compiler-rt might provide them, but I don't believe I have them in spite of building compiler-rt. I'll look at this again and see if maybe I need to tweak my compiler-rt build to get it to generate or install them in the right place.

https://github.com/llvm/llvm-project/pull/85089