test: include common.h in errors.h

We need common.h to define what GIT_EXTERN() is so the parser doesn't
bail on us.
test: we now detect more uses

I'm not entirely sure why the old code doesn't detect these uses.
test: skip ones for creation of enums

We don't currently auto-create enums from defines, and we cannot get
documentation for them from clang, so we probably won't in the future
either.

For now skip those tests that rely on that.