S390: Configure check for vector support in gcc.

S390: Configure check for vector support in gcc.

The S390 specific test checks if the gcc has support for vector registers
by compiling an inline assembly which clobbers vector registers.
On success the macro HAVE_S390_VX_GCC_SUPPORT is defined.
This macro can be used to determine if e.g. clobbering vector registers
is allowed or not.

ChangeLog:

	* config.h.in (HAVE_S390_VX_GCC_SUPPORT): New macro undefine.
	* sysdeps/s390/configure.ac: Add test for S390 vector register
	support in gcc.
	* sysdeps/s390/configure: Regenerated.