testsuite: Fix excess errors for new modules testcases on powerpc [PR114320]

On some configurations, PowerPC emits -Wpsabi warnings when using IEEE
long doubles on a machine configured with IBM long double by default.
This patch suppresses these warnings for this testcase.

	PR testsuite/114320

gcc/testsuite/ChangeLog:

	* g++.dg/modules/target-powerpc-1_a.C: Suppress -Wpsabi.
	* g++.dg/modules/target-powerpc-1_b.C: Likewise.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>