i386 and m68k architectures should use math-use-builtins-sqrt.h rather
than relying on architecture-specific or inline assembly implementations.
The PowerPC optimization for PPC 601/603 (30 years old) is removed.
Tested on x86_64-linux-gnu and i686-linux-gnu.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>