S390: Move utf8-utf16-z9.c to multiarch folder and use s390_libc_ifunc_expr macro.

S390: Move utf8-utf16-z9.c to multiarch folder and use s390_libc_ifunc_expr macro.

The utf8-utf16-z9.c iconv module is using ifunc and thus the ifunc part should
be in multiarch folder.  Otherwise ifunc is used even if you configure
with --disable-multi-arch.

This patch moves the ifunc resolvers to the new file
sysdeps/s390/multiarch/utf8-utf16-z9.c. The resolvers are now implemented
with s390_libc_ifunc_expr macro instead of using gcc attribute ifunc directly.

The ifunc versions are implemented in sysdeps/s390/utf8-utf16-z9.c.
Each version is only implemented if needed or supported.  Therefore there is
a block at beginning of the file which selects the versions which should be
defined depending on support for multiarch, vector-support and used minimum
architecture level.  This block defines HAVE_[FROM|TO]_[C|CU|VX] to 1 or 0.
The code below is rearranged and surrounded
by #if HAVE_[FROM|TO]_[C|CU|VX] == 1.  There is no functional change.

The cu instructions are z9 zarch instructions.  As the major distros are
already using the newer z196 as architecture level set, those instructions
can be used as fallback version instead of the c-code.  This behaviour is
decided at compile time via HAVE_S390_MIN_Z196_ZARCH_ASM_SUPPORT.

ChangeLog:

	* sysdeps/s390/multiarch/utf8-utf16-z9.c: New File.
	* sysdeps/s390/utf8-utf16-z9.c: Move ifunc resolvers to multiarch
	folder and define ifunc versions depending on HAVE_[FROM|TO]_[C|CU|VX].
	(HAVE_FROM_C, HAVE_FROM_CU, HAVE_FROM_VX, HAVE_TO_C, HAVE_TO_VX,
	FROM_LOOP_DEFAULT, FROM_LOOP_C, FROM_LOOP_CU, FROM_LOOP_VX,
	TO_LOOP_DEFAULT, TO_LOOP_C, TO_LOOP_VX): New Define.