decay vect tests from run to link for pr95401

decay vect tests from run to link for pr95401

When vect.exp finds our configuration disables altivec by default, it
disables the execution of vectorization tests, assuming the test
hardware doesn't support it.

Tests become just compile tests, but compile tests won't work
correctly when additional sources are named, e.g. pr95401.cc, because
GCC refuses to compile multiple files into the same asm output.

With this patch, the default for when execution is not possible
becomes link.

for  gcc/testsuite/ChangeLog

	* lib/target-supports.exp (check_vect_support_and_set_flags):
	Decay to link rather than compile.