ppc: testsuite: vec-mul requires vsx runtime

ppc: testsuite: vec-mul requires vsx runtime

vec-mul is an execution test, but it only requires a powerpc_vsx_ok
effective target, which is enough only for compile tests.  In order to
check for runtime and execution environment support, we need to
require vsx_hw.  Make that a condition for execution, but still
perform a compile test if the condition is not satisfied.

for  gcc/testsuite/ChangeLog

	* gcc.target/powerpc/vec-mul.c: Run on target vsx_hw, just
	compile otherwise.