287254 by pfg:
Be more GCC-friendly with attributes
Being clang the default compiler, we were always giving precedence to
the __has_attribute check. Unfortunately clang generally doesn't support
the new attributes (alloc_size was briefly supported and then reverted)
so we were always doing both checks. Give the precedence to GCC as that is
the working case now.
Do the same for __has_builtin() for consistency.
287253 by imp:
Fix cleaning of files generated from .m sources.