S390: Do not set FE_INEXACT with feraiseexcept (FE_OWERFLOW|FE_UNDERFLOW).

S390: Do not set FE_INEXACT with feraiseexcept (FE_OWERFLOW|FE_UNDERFLOW).

On s390 feraiseexcept (FE_OVERFLOW|FE_UNDERFLOW) sets FE_INEXACT, too.
This patch uses z196 zarch load rounded instruction which can suppress
FE_INEXACT exception if gcc has z196 support in used configuration.
Otherwise FE_INEXACT flag is set as before. The gcc support is tested
in a new configure-check.

A comment in fsetexcptflg.c is corrected as new exceptions are not
executed with the next floating-point instruction if fpc is set with
_FPU_SETCW macro. It seems the comment was copied e.g. from
sysdeps/x86_64/fpu/fsetexcptflg.c file.

ChangeLog:

	* config.h.in (HAVE_S390_MIN_Z196_ZARCH_ASM_SUPPORT):
	New undefine.
	* sysdeps/s390/configure.ac: Add test for z196 zarch support.
	* sysdeps/s390/configure: Regenerated.
	* sysdeps/s390/fpu/fraiseexcpt.c (__feraiseexcept): Use ledbra
	instruction for raising over-/underflow if z196 zarch is supported
	by default.
	* sysdeps/s390/fpu/fsetexcptflg.c (fesetexceptflag):
	Correct comment.