[clang] [clang][scan-build] Treat --use-cc and --use-c++ as shell commands (PR #131932)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat approved this pull request.

Overall I'm satisfied with the direction of the commit and I agree that explicitly specifying an invalid compiler should be a hard error. (I could also accept a warning as long as it's loud and visible, but the current "silently use the default" behavior is terrible and must be replaced.)

https://github.com/llvm/llvm-project/pull/131932