S390: configure check for vector instruction support in assembler.

S390: configure check for vector instruction support in assembler.

The S390 specific test checks if the assembler has support for the new z13
vector instructions by compiling a vector instruction. The .machine and
.machinemode directives are needed to compile the vector instruction without
-march=z13 option on 31/64 bit.
On success the macro HAVE_S390_VX_ASM_SUPPORT is defined. This macro is used
to determine if the optimized functions can be build without compile errors.
If the used assembler lacks vector support, then a warning is dumped while
configuring and only the common code functions are build.

The z13 instruction support was introduced in
"[Committed] S/390: Add support for IBM z13."
(https://sourceware.org/ml/binutils/2015-01/msg00197.html)

ChangeLog:

	* config.h.in (HAVE_S390_VX_ASM_SUPPORT): New macro undefine.
	* sysdeps/s390/configure.ac: Add test for S390 vector instruction
	assembler support.
	* sysdeps/s390/configure: Regenerated.