[clang] Support target names with dots in more utilities (PR #65812)

[via cfe-commits]

dankm wrote:

> Do any others exist on other platforms?

I don't know. I explicitly tested that `.sh` remains, but that was just because it's relatively common (in my experience) to see tools like clang wrapped in a shell script. On Windows there are several executable extensions but I think the only one that makes sense in our use case is `.exe`, though `.ex_` might also be a possibility.

https://github.com/llvm/llvm-project/pull/65812