Define AO_TS_SET as __GCC_ATOMIC_TEST_AND_SET_TRUEVAL if applicable

Define AO_TS_SET as __GCC_ATOMIC_TEST_AND_SET_TRUEVAL if applicable

* src/atomic_ops/sysdeps/gcc/aarch64.h (AO_GCC_ATOMIC_TEST_AND_SET):
Define (before include test_and_set_t_is_ao_t.h).
* src/atomic_ops/sysdeps/gcc/nios2.h (AO_GCC_ATOMIC_TEST_AND_SET):
Likewise.
* src/atomic_ops/sysdeps/test_and_set_t_is_ao_t.h: Refine comment.
* src/atomic_ops/sysdeps/test_and_set_t_is_char.h: Likewise.
* src/atomic_ops/sysdeps/test_and_set_t_is_ao_t.h (AO_TS_SET_TRUEVAL):
New internal macro (defined via __GCC_ATOMIC_TEST_AND_SET_TRUEVAL).
* src/atomic_ops/sysdeps/test_and_set_t_is_char.h (AO_TS_SET_TRUEVAL):
Likewise.
* src/atomic_ops/sysdeps/test_and_set_t_is_ao_t.h (AO_TS_val): Use
AO_TS_SET_TRUEVAL instead of 1.
* src/atomic_ops/sysdeps/test_and_set_t_is_char.h (AO_BYTE_TS_val):
Use AO_TS_SET_TRUEVAL instead of 0xff; reformat code.
* src/atomic_ops/sysdeps/test_and_set_t_is_char.h (AO_TS_t): Move down
(to be after AO_TS_SET).