X86-64: Prepare memmove-vec-unaligned-erms.S

Prepare memmove-vec-unaligned-erms.S to make the SSE2 version as the
default memcpy, mempcpy and memmove.

	* sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
	(MEMCPY_SYMBOL): New.
	(MEMPCPY_SYMBOL): Likewise.
	(MEMMOVE_CHK_SYMBOL): Likewise.
	Replace MEMMOVE_SYMBOL with MEMMOVE_CHK_SYMBOL on __mempcpy_chk
	symbols.  Replace MEMMOVE_SYMBOL with MEMPCPY_SYMBOL on
	__mempcpy symbols.  Provide alias for __memcpy_chk in libc.a.
	Provide alias for memcpy in libc.a and ld.so.