`check_names.py` cannot have function-name exceptions

[davidhorstmann-arm]

The comment //no-check-names is supposed to neutralise name checks, but it doesn't work with function names.

This is slightly more complicated to implement than for macros as we do checks on function names then we use nm to check that no symbols are exposed externally that are not declared in headers. We would have to scan for the comment and then remember which function names do not need checking.

With this in mind, would the ability to turn this off even be desirable?

[gilles-peskine-arm]

Nowadays I suspect that clang-tidy's readability-identifier-naming
check can do what we do with check-names. We should consider this before adding more features to check-names.