This also helps document glibc’s direction in using GCC’s
memory-allocation checking.
* lib/cdefs.h: Omit comments that glibc rejected.
(__returns_nonnull, __attr_access_none, __attr_dealloc)
(__attr_dealloc_free): New macros.
* lib/libc-config.h: Undef the new macros that are defined
unconditionally.
* lib/malloc/dynarray_at_failure.c [_LIBC]: Do not include stdlib.h.
(__libc_dynarray_at_failure) [_LIBC]: Call __libc_fatal,
fixing a bad merge previously.