[7.1.0] Mark gcc-<version> as `gcc` instead of `compiler` in Unix CC toolchain (#21224)

Fixes #17794

I was looking at writing a test for this, but not sure how you'd like me
to go about that. Hard-code a gcc, e.g. `gcc-11`, or search the `$PATH`
for a `gcc-<version>`?
    
Closes #20350.

Commit
https://github.com/bazelbuild/bazel/commit/88771830d92a93027ed7dfb5d130b3311400dbc4
    
PiperOrigin-RevId: 604543138
Change-Id: I71ebbac77e4e32ebc5d99ec4a81415727af12cbc