[Bug testsuite/114842] New: rs6000: Adjust some test cases with powerpc_vsx_ok

["linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114842

            Bug ID: 114842
           Summary: rs6000: Adjust some test cases with powerpc_vsx_ok
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: testsuite
          Assignee: unassigned at gcc dot gnu.org
          Reporter: linkw at gcc dot gnu.org
  Target Milestone: ---

The current effective target powerpc_vsx_ok is mainly to check if it's fine to
specify -mvsx (without any warnings etc.) and can finally result in a object
file (it means the underlying environment like assembler supports vsx insns).
But most of the test cases being guarded with this checking actually want to
check if VSX feature is enabled, such as: the wanted behavior only happens with
VSX feature enabled. When users specifying -mno-vsx in RUNTESTFLAGS, it can
disable VSX feature (with some old runtest, -mno-vsx comes after -mvsx), but
powerpc_vsx_ok checking will still pass as it's fine to specify -mvsx, so if
the test case doesn't have explicit -mvsx, then the given -mno-vsx can disable
VSX feature and make that test case fail, meanwhile even if the test case has
specified -mvsx explicitly it would fail with old runtest as -mno-vsx comes
last. We already have another effective target powerpc_vsx which effectively
checks for VSX enabled, so we should update most of test case to adopt it
instead.