selftests/powerpc: Handle Makefile for unrecognized option

On older distributions like Sles12SP5 gcc does not recognize
-no-pie option making the powerpc selftests build to fail

Fixes the following:
gcc: error: unrecognized command line option ‘-no-pie’

Signed-off-by: Harish <harish@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191113094219.14946-1-harish@linux.ibm.com