[clang] [llvm] [AArch64][Driver] Fix behavior of +nofeat modifier on -mcpu (PR #203458)

[via cfe-commits]

yamash-fj wrote:

> I found the existing test about `-march` `+nofeat` behavior and it appears to be covered by those tests, for example in `clang/test/Driver/aarch64-negative-modifiers-for-default-features.c`.

Since that file covers negative modifiers with ``-march``, it may be better to add ``-mcpu`` tests to that file rather than keeping them in a separate test file. What do you think?

https://github.com/llvm/llvm-project/pull/203458