rs6000/test: Adjust some test cases on partial vector [PR96373]

rs6000/test: Adjust some test cases on partial vector [PR96373]

As Richard pointed out in [1] and the testing on Power10, the
proposed fix for PR96373 requires some updates on a few rs6000
test cases which adopt partial vector.  This patch is to fix
all of them with one extra option "-fno-trapping-math" as
Richard suggested.

Besides, the original test case also failed on Power10 without
Richard's proposed fix, this patch adds it together for a bit
better testing coverage.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2023-January/610728.html

	PR target/96373

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/p9-vec-length-epil-1.c: Add -fno-trapping-math.
	* gcc.target/powerpc/p9-vec-length-epil-2.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-epil-3.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-epil-4.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-epil-5.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-epil-6.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-epil-8.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-1.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-2.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-3.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-4.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-5.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-6.c: Likewise.
	* gcc.target/powerpc/p9-vec-length-full-8.c: Likewise.
	* gcc.target/powerpc/pr96373.c: New test.