i386: memcpy functions with SSE2 unaligned load/store

These new memcpy functions are the 32-bit version of x86_64 SSE2 unaligned
memcpy.  Memcpy average performace benefit is 18% on Silvermont, other
platforms also improved about 35%, benchmarked on Silvermont, Haswell, Ivy
Bridge, Sandy Bridge and Westmere, performance results attached in

https://sourceware.org/ml/libc-alpha/2014-07/msg00157.html

	* sysdeps/i386/i686/multiarch/bcopy-sse2-unaligned.S: New file.
	* sysdeps/i386/i686/multiarch/memcpy-sse2-unaligned.S: Likewise.
	* sysdeps/i386/i686/multiarch/memmove-sse2-unaligned.S: Likewise.
	* sysdeps/i386/i686/multiarch/mempcpy-sse2-unaligned.S: Likewise.
	* sysdeps/i386/i686/multiarch/bcopy.S: Select the sse2_unaligned
	version if bit_Fast_Unaligned_Load is set.
	* sysdeps/i386/i686/multiarch/memcpy.S: Likewise.
	* sysdeps/i386/i686/multiarch/memcpy_chk.S: Likewise.
	* sysdeps/i386/i686/multiarch/memmove.S: Likewise.
	* sysdeps/i386/i686/multiarch/memmove_chk.S: Likewise.
	* sysdeps/i386/i686/multiarch/mempcpy.S: Likewise.
	* sysdeps/i386/i686/multiarch/mempcpy_chk.S: Likewise.
	* sysdeps/i386/i686/multiarch/Makefile (sysdep_routines): Add
	bcopy-sse2-unaligned, memcpy-sse2-unaligned,
	memmove-sse2-unaligned and mempcpy-sse2-unaligned.
	* sysdeps/i386/i686/multiarch/ifunc-impl-list.c (MAX_IFUNC): Set
	to 4.
	(__libc_ifunc_impl_list): Test __bcopy_sse2_unaligned,
	__memmove_chk_sse2_unaligned, __memmove_sse2_unaligned,
	__memcpy_chk_sse2_unaligned, __memcpy_sse2_unaligned,
	__mempcpy_chk_sse2_unaligned, and __mempcpy_sse2_unaligned.