IBM Z: Preserve exceptions in autovec-*-signaling-eq.c tests

IBM Z: Preserve exceptions in autovec-*-signaling-eq.c tests

DSE, DCE, and other passes are removing redundant signaling comparisons
from these tests, but the whole point is to check that GCC knows how to
emit them.  Use -fno-delete-dead-exceptions to prevent that.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/zvector/autovec-double-signaling-eq.c:
	Preserve exceptions.
	* gcc.target/s390/zvector/autovec-float-signaling-eq.c:
	Likewise.