[clang] [Driver] Add winsysroot alias to the GNU driver (PR #95320)

[Saleem Abdulrasool via cfe-commits]

compnerd wrote:

@zmodem - they are aliases after all. I think that core logic being tested is sufficient. I can see the value in testing that the flags are honoured, but the tests would be of low value IMO. They just test the flags are listed.

https://github.com/llvm/llvm-project/pull/95320