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

[David Spickett via cfe-commits]

================
@@ -0,0 +1,31 @@
+// RUN: %clang --target=aarch64-linux-gnu -mcpu=neoverse-v2 %s -### 2>&1 | FileCheck %s --check-prefix=NEOVERSE-V2-DEFAULT
----------------
DavidSpickett wrote:

This file should have at least a header comment stating what you are checking for, for instance:
```
/// Check that +no<feature> removes the feature even if the feature is implied by .... <and so on>
```
In theory people can git blame to find your commit message, but sometimes that single sentence can really help triage.

And just glancing at the tests, I don't see why there are so many. Adding a few for coverage is ok, but if some are for specific corner cases you should also add a comment to them.

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