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.
