testsuite: LoongArch: Enable 16B atomic tests if the test machine supports LSX and SCQ

testsuite: LoongArch: Enable 16B atomic tests if the test machine supports LSX and SCQ

Enable those tests so we won't make too stupid mistakes in 16B atomic
implementation anymore.

All these test passed on a Loongson 3C6000/S except
atomic-other-int128.c.  With GDB patched to support sc.q
(https://sourceware.org/pipermail/gdb-patches/2025-August/220034.html)
this test also XPASS.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp
	(check_effective_target_loongarch_scq_hw): New.
	(check_effective_target_sync_int_128_runtime): Return 1 on
	loongarch64-*-* if hardware supports both LSX and SCQ.
	* gcc.dg/atomic-compare-exchange-5.c: Pass -mlsx -mscq for
	loongarch64-*-*.
	* gcc.dg/atomic-exchange-5.c: Likewise.
	* gcc.dg/atomic-load-5.c: Likewise.
	* gcc.dg/atomic-op-5.c: Likewise.
	* gcc.dg/atomic-store-5.c: Likewise.
	* gcc.dg/atomic-store-6.c: Likewise.
	* gcc.dg/simulate-thread/atomic-load-int128.c: Likewise.
	* gcc.dg/simulate-thread/atomic-other-int128.c: Likewise.
	(dg-final): xfail on loongarch64-*-* because  gdb does not
	handle sc.q properly yet.