silence expected psabi warning in ipa-sra-19 on ppc-vxworks

silence expected psabi warning in ipa-sra-19 on ppc-vxworks

The default CPU for our ppc-vx7r2 toolchain has no support for altivec
or vsx, so an ABI without vector support is selected.  The selected
calling conventions do not cover passing or returning vector types, so
-Wpsabi warns about such uses.

powerpc-ibm-aix* already silences these warnings with -Wno-psabi;
this patch extends that to powerpc-wrs-vxworks* too.

for  gcc/testsuite/ChangeLog

	* gcc.dg/ipa/ipa-sra-19.c: Extend -Wno-psabi to ppc-vx7r2.