fpending, obstack, strerror-override: use pure+const function attrs * lib/fpending.h (__fpending): Declare with the "pure" attribute. * lib/obstack.c (_obstack_allocated_p): Likewise. * lib/obstack.h (_obstack_memory_used): Likewise. (_obstack_memory_used): Likewise. * lib/strerror-override.h (strerror_override): Declare with the "const" attribute.