Set NOPIE_CFLAGS and NOPIE_LDFLAGS

Set NOPIE_CFLAGS and NOPIE_LDFLAGS

GCC 6 can be configured to generate PIE by default.  But some linker
size tests expect non-PIE.  This patch defines NOPIE_CFLAGS to
"-fno-PIE" and NOPIE_LDFLAGS to "-no-pie" if target compiler supports
them.  Add $NOPIE_CFLAGS and $NOPIE_LDFLAGS to linker size tests if
needed.

	* config/default.exp (NOPIE_CFLAGS): New.
	(NOPIE_LDFLAGS): Likewise.
	* ld-size/size.exp (run_cc_link_tests): Add $NOPIE_CFLAGS and
	$NOPIE_LDFLAGS if needed.
	(run_ld_link_exec_tests): Add $NOPIE_CFLAGS if needed.