S390: Optimize memchr, rawmemchr and wmemchr.

S390: Optimize memchr, rawmemchr and wmemchr.

This patch provides optimized versions of memchr, rawmemchr and wmemchr with the
z13 vector instructions.

ChangeLog:

	* sysdeps/s390/multiarch/memchr-vx.S: New File.
	* sysdeps/s390/multiarch/memchr.c: Likewise.
	* sysdeps/s390/multiarch/rawmemchr-c.c: Likewise.
	* sysdeps/s390/multiarch/rawmemchr-vx.S: Likewise.
	* sysdeps/s390/multiarch/rawmemchr.c: Likewise.
	* sysdeps/s390/multiarch/wmemchr-c.c: Likewise.
	* sysdeps/s390/multiarch/wmemchr-vx.S: Likewise.
	* sysdeps/s390/multiarch/wmemchr.c: Likewise.
	* sysdeps/s390/s390-32/multiarch/memchr.c: Likewise.
	* sysdeps/s390/s390-64/multiarch/memchr.c: Likewise.
	* sysdeps/s390/multiarch/Makefile (sysdep_routines): Add memchr, wmemchr
	and rawmemchr functions.
	* sysdeps/s390/multiarch/ifunc-impl-list-common.c
	(__libc_ifunc_impl_list_common): Add ifunc test for memchr, rawmemchr
	and wmemchr.
	* wcsmbs/wmemchr.c: Use WMEMCHR if defined.
	* string/test-memchr.c: Add wmemchr support.
	* wcsmbs/test-wmemchr.c: New File.
	* wcsmbs/Makefile (strop-tests): Add wmemchr.
	* benchtests/bench-memchr.c: Add wmemchr support.
	* benchtests/bench-wmemchr.c: New File.
	* benchtests/Makefile (wcsmbs-bench): wmemchr.