[llvm] [RuntimeLibCalls] Consistently disable unavailable libcalls (PR #116214)

[Nikita Popov via llvm-commits]

nikic wrote:

> Thanks for looking into this. The CI shows an XCore test failing but only on Windows.

I've fixed this by using `-mtriple` instead of `-march` in that test. `-march` keeps the rest of the Windows triple, which isn't something that makes sense for xcore.

https://github.com/llvm/llvm-project/pull/116214