i386: Don't define multiarch __memmove_chk in libc.a [BZ #21791]

There is no need to define multiarch __memmove_chk in libc.a since they
aren't used at all.

	[BZ #21791]
	* sysdeps/i386/i686/multiarch/memcpy-sse2-unaligned.S
	(MEMCPY_CHK): Define only if SHARED is defined.
	* sysdeps/i386/i686/multiarch/memcpy-ssse3-rep.S (MEMCPY_CHK):
	Likewise.
	* sysdeps/i386/i686/multiarch/memcpy-ssse3.S (MEMCPY_CHK):
	Likewise.