testsuite, rs6000: Adjust pcrel-sibcall-1.c with noipa [PR112751]

As PR112751 shows, commit r14-5628 caused pcrel-sibcall-1.c
to fail as it enables ipa-vrp which makes return values of
functions {x,y,xx} as known and propagated.  This patch is
to adjust it with noipa to make it not fragile.

	PR testsuite/112751

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pcrel-sibcall-1.c: Replace noinline as noipa.