[flang][msvc] Do not use gcc/clang command line options for msvc.
The command line options -Wno-error and -Wno-unused-parameter are specific to gcc/clang, do not use them when compiling with other compilers.
This patch is part of the series to make flang compilable with MS Visual Studio.
Reviewed By: isuruf
Differential Revision: https://reviews.llvm.org/D85355