testsuite, rs6000: Make powerpc_altivec consider current_compiler_flags [PR114842]

testsuite, rs6000: Make powerpc_altivec consider current_compiler_flags [PR114842]

As noted in PR114842, most of the test cases which require
effective target check powerpc_altivec_ok actually care
about if ALTIVEC feature is enabled, and they should adopt
effective target powerpc_altivec instead.  By considering
we already have a number of test cases having explicit
-maltivec in dg-options etc., to keep them still be tested
as before even without altivec enabled by default, this
patch makes powerpc_altivec consider current_compiler_flags
like what we do for powerpc_vsx.

	PR testsuite/114842

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp (check_effective_target_powerpc_altivec):
	Take current_compiler_flags into account.