[clang] [llvm] Use %errc to get text for system errors (PR #109852)

[Sean Perry via llvm-commits]

perry-ca wrote:

Thanks for the offer David.  I do have permission now.  I held off merging yesterday because the builds were all broken from some other change.  The builds all pass now.  I'll merge it.

https://github.com/llvm/llvm-project/pull/109852