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