[clang] Make `-fvisibility={}` and `-ftype-visibility={}` benign options. (#71985)

Both options do not affect the AST content that is serialized into the PCM. This
commit includes the following changes:
    
1.) Mark `-fvisibility={}` and `-ftype-visibility={}` as benign options.That
     means they are no longer considered part of the module hash, which can
     reduce the number of module variants.
    
2.) Add a test to verify the generated LLVM IR is not affected by the default
     visibiliy mode in the module.

3.) Add a test to clang-scan-deps to ensure only one module is build, even if
      the above mentioned options are used.
    
This fixes rdar://118246054.