ctest: fix bug where functions and statics aren't skipped

[mbyx]

Description

Fixed extern fns and extern statics not being skipped properly. Also added a rename_alias method that should be preferred to be used over rename_type.

Sources

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[tgross35]

Could you add a test case for this? Add a skip to one of the bless tests so we know if it changes in the future

[tgross35]

Also, can rename_type just be deleted here? Assuming its functionality is now covered by the split rename_* functions

[mbyx]

I don't think rename_type can be deleted. rename_alias would only work for MapInput items that are passed as MapInput::Alias, so it only affects the alias tests. But if some other test uses for example *const type_alias (or even just field: type_alias), then that is regarded as a MapInput::Type, so rename_alias wouldn't work.

Definitely something to be improved, since that part of the codebase is definitely the most buggy.