libstdc++: Add dg-require-thread-fence in several tests

libstdc++: Add dg-require-thread-fence in several tests

Some targets like arm-eabi with newlib and default settings rely on
__sync_synchronize() to ensure synchronization.  Newlib does not
implement it by default, to make users aware they have to take special
care.

This makes a few tests fail to link.

This patch requires the missing thread-fence effective target in the
tests that need it, making them UNSUPPORTED instead of FAIL and
UNRESOLVED.

2023-09-10  Christophe Lyon  <christophe.lyon@linaro.org>

	libstdc++-v3/
	* testsuite/29_atomics/atomic/compare_exchange_padding.cc: Likewise.
	* testsuite/29_atomics/atomic/cons/value_init.cc: Likewise.
	* testsuite/29_atomics/atomic_float/value_init.cc: Likewise.
	* testsuite/29_atomics/atomic_integral/cons/value_init.cc: Likewise.
	* testsuite/29_atomics/atomic_ref/compare_exchange_padding.cc: Likewise.
	* testsuite/29_atomics/atomic_ref/generic.cc: Likewise.
	* testsuite/29_atomics/atomic_ref/integral.cc: Likewise.
	* testsuite/29_atomics/atomic_ref/pointer.cc: Likewise.