Define AO_TS_SET to true (1) if GCC atomic_test_and_set is used

Define AO_TS_SET to true (1) if GCC atomic_test_and_set is used
(fix commit 3315a03)

According to GCC manual about the built-in functions for memory model
aware atomic operations, __atomic_test_and_set returns bool value;
bool true is encoded as 1.

* src/atomic_ops/sysdeps/test_and_set_t_is_char.h [AO_PREFER_GENERALIZED
|| !__GCC_ATOMIC_TEST_AND_SET_TRUEVAL] (AO_TS_SET_TRUEVAL): Define to 1
(instead of 0xff).