[PATCH,rs6000] Testsuite fixup pr96139 tests

[PATCH,rs6000] Testsuite fixup pr96139 tests

Hi,
  As reported, the recently added pr96139 tests will fail on older targets
  because the tests are missing the appropriate -mvsx or -maltivec options.
  This adds the options and clarifies the dg-require statements.

  The pr96139-c.c test needs -maltivec to work, but does not actually use
  vectors, so does not require -mvsx like the others.

  Sniff-regtested OK when specifying older targets on a power7 host.
  --target_board=unix/'{-mcpu=power4,-mcpu=power5,-mcpu=power6,-mcpu=power7,
  -mcpu=power8,-mcpu=power9}''{-m64,-m32}'"

gcc/testsuite/ChangeLog:
	* gcc.target/powerpc/pr96139-a.c: Specify -mvsx option and update the
	dg-require stanza to match.
	* gcc.target/powerpc/pr96139-b.c: Same.
	* gcc.target/powerpc/pr96139-c.c: Specify -maltivec option and update
	the dg-require stanza to match.