rs6000: Fix the vec-adde* testcases once more

rs6000: Fix the vec-adde* testcases once more

David found the vec-adde{,c}-int128.c testcases fail on AIX.  Those
tests should only run on targets that have int128.

This also changes the non-int128 testcases to check for the hardware
they require.

gcc/testsuite/
	* gcc.target/powerpc/vec-adde-int128.c: Only run if int128 exists.
	* gcc.target/powerpc/vec-addec-int128.c: Ditto.
	* gcc.target/powerpc/vec-adde.c: Require vsx_hw, don't require a
	64-bit default target.
	* gcc.target/powerpc/vec-addec.c: Require p8vector_hw, don't require
	a 64-bit default target.

From-SVN: r245453