Check Prefer_ERMS in memmove/memcpy/mempcpy/memset

Although the Enhanced REP MOVSB/STOSB (ERMS) implementations of memmove,
memcpy, mempcpy and memset aren't used by the current processors, this
patch adds Prefer_ERMS check in memmove, memcpy, mempcpy and memset so
that they can be used in the future.

	* sysdeps/x86/cpu-features.h (bit_arch_Prefer_ERMS): New.
	(index_arch_Prefer_ERMS): Likewise.
	* sysdeps/x86_64/multiarch/memcpy.S (__new_memcpy): Return
	__memcpy_erms for Prefer_ERMS.
	* sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
	(__memmove_erms): Enabled for libc.a.
	* ysdeps/x86_64/multiarch/memmove.S (__libc_memmove): Return
	__memmove_erms or Prefer_ERMS.
	* sysdeps/x86_64/multiarch/mempcpy.S (__mempcpy): Return
	__mempcpy_erms for Prefer_ERMS.
	* sysdeps/x86_64/multiarch/memset.S (memset): Return
	__memset_erms for Prefer_ERMS.