S390: Refactor wcscmp ifunc handling.

S390: Refactor wcscmp ifunc handling.

The ifunc handling for wcscmp is adjusted in order to omit ifunc
variants if those will never be used as the minimum architecture level
already supports newer CPUs by default.
Glibc internal calls will then also use the "newer" ifunc variant.

ChangeLog:

	* sysdeps/s390/multiarch/Makefile
	(sysdep_routines): Remove wcscmp variants.
	* sysdeps/s390/Makefile (sysdep_routines): Add wcscmp variants.
	* sysdeps/s390/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Refactor ifunc handling for wcscmp.
	* sysdeps/s390/multiarch/wcscmp-c.c: Move to ...
	* sysdeps/s390/wcscmp-c.c: ... here and adjust ifunc handling.
	* sysdeps/s390/multiarch/wcscmp-vx.S: Move to ...
	* sysdeps/s390/wcscmp-vx.S: ... here and adjust ifunc handling.
	* sysdeps/s390/multiarch/wcscmp.c: Move to ...
	* sysdeps/s390/wcscmp.c: ... here and adjust ifunc handling.
	* sysdeps/s390/ifunc-wcscmp.h: New file.