[aarch64] Add memchr.

2014-07-11  Kévin Petit  <kevin.petit@arm.com>

	* libc/machine/aarch64/memchr.S: New file.
	* libc/machine/aarch64/memchr-stub.c: New file.
	* libc/machine/aarch64/Makefile.am: Add the new files.
	* libc/machine/aarch64/Makefile.in: Regenerated.