PR92398: Fix testcase failure of pr72804.c

PR92398: Fix testcase failure of pr72804.c

P9LE generated instruction is not worse than P8LE.
mtvsrdd;xxlnot;stxv vs. not;not;std;std.
It can have longer latency, but latency via memory is not so critical,
and this does save decode and other resources.  It's hard to choose
which is best.  Update the test case to fix failures.

gcc/testsuite/ChangeLog:

	2019-12-02  Luo Xiong Hu  <luoxhu@linux.ibm.com>

	PR testsuite/92398
	* gcc.target/powerpc/pr72804.c: Split the store function to...
	* gcc.target/powerpc/pr92398.h: ... this one.  New.
	* gcc.target/powerpc/pr92398.p9+.c: New.
	* gcc.target/powerpc/pr92398.p9-.c: New.
	* lib/target-supports.exp (check_effective_target_p8): New.
	(check_effective_target_p9+): New.

From-SVN: r278890