Add a simple rawmemchr implementation. Use strlen for rawmemchr(s, '\0') as it

is the fastest way to search for '\0'.  Otherwise use memchr with an infinite
size.  This is 3x faster on benchtests for large sizes.  Passes GLIBC tests.

	* sysdeps/aarch64/rawmemchr.S (__rawmemchr): New file.
	* sysdeps/aarch64/strlen.S (__strlen): Change to __strlen to avoid PLT.