s390: Refactor ifunc resolvers due to false debuginfo.

s390: Refactor ifunc resolvers due to false debuginfo.

This patch adjusts the s390 specific ifunc helper macros in ifunc-resolve.h to
use the common __ifunc macro, which uses gcc attribute ifunc to get rid of the
false debuginfo. Therefore the redirection construct is applied where needed.

Perhaps in future we can switch some of the internal symbols __GI_* from the
fallback variant to the ifunc function. But this change is not
straightforward due to a segmentation fault while linking libc.so with older
binutils on s390.

ChangeLog:

	[BZ #20478]
	* sysdeps/s390/multiarch/ifunc-resolve.h
	(s390_vx_libc_ifunc2, s390_libc_ifunc): Use __ifunc from libc-symbols.h
	to create ifunc symbols.
	(s390_vx_libc_ifunc_init, s390_vx_libc_ifunc_redirected
	, s390_vx_libc_ifunc2_redirected, s390_libc_ifunc_init): New define.
	* sysdeps/s390/multiarch/memchr.c: Redirect ifunced function in header
	for using it as type for ifunc function.
	* sysdeps/s390/multiarch/mempcpy.c: Likewise.
	* sysdeps/s390/multiarch/rawmemchr.c: Likewise.
	* sysdeps/s390/multiarch/stpcpy.c: Likewise.
	* sysdeps/s390/multiarch/stpncpy.c: Likewise.
	* sysdeps/s390/multiarch/strcat.c: Likewise.
	* sysdeps/s390/multiarch/strchr.c: Likewise.
	* sysdeps/s390/multiarch/strcmp.c: Likewise.
	* sysdeps/s390/multiarch/strcpy.c: Likewise.
	* sysdeps/s390/multiarch/strcspn.c: Likewise.
	* sysdeps/s390/multiarch/strlen.c: Likewise.
	* sysdeps/s390/multiarch/strncmp.c: Likewise.
	* sysdeps/s390/multiarch/strncpy.c: Likewise.
	* sysdeps/s390/multiarch/strnlen.c: Likewise.
	* sysdeps/s390/multiarch/strpbrk.c: Likewise.
	* sysdeps/s390/multiarch/strrchr.c: Likewise.
	* sysdeps/s390/multiarch/strspn.c: Likewise.
	* sysdeps/s390/multiarch/wcschr.c: Likewise.
	* sysdeps/s390/multiarch/wcscmp.c: Likewise.
	* sysdeps/s390/multiarch/wcspbrk.c: Likewise.
	* sysdeps/s390/multiarch/wcsspn.c: Likewise.
	* sysdeps/s390/multiarch/wmemchr.c: Likewise.
	* sysdeps/s390/multiarch/wmemset.c: Likewise.
	* sysdeps/s390/s390-32/multiarch/memcmp.c: Likewise.
	* sysdeps/s390/s390-32/multiarch/memcpy.c: Likewise.
	* sysdeps/s390/s390-32/multiarch/memset.c: Likewise.
	* sysdeps/s390/s390-64/multiarch/memcmp.c: Likewise.
	* sysdeps/s390/s390-64/multiarch/memcpy.c: Likewise.
	* sysdeps/s390/s390-64/multiarch/memset.c: Likewise.