Switching language to C does not change language standard

[ThadHouse]

Trying to parse a file as C just by using -x c results in the following error

  error: invalid argument '--std=c++17' not allowed with 'C'

ClangSharp should be smart enough to switch std to c17 when the language is switched to C.

[tannergooding]

This is probably a disconnect here: https://github.com/microsoft/ClangSharp/blob/main/sources/ClangSharpPInvokeGenerator/Program.cs#L438-L439
It's probably ending up as -x c --std c++17 and clang treats that as C++17