rs6000: Fix altivec-7.c testcase

It currently wants to see lvx insns on AIX, and no lvx insns on Linux.
What is really wanted is lvx insns when no VSX, and lxv* insns if VSX.
This fixes it.


	* gcc.target/powerpc/altivec-7.c: Look for lxv* if generating VSX
	instructions, and lvx if not.

From-SVN: r269772