Add AO_GENERALIZE_ASM_BOOL_CAS new macro to allow AO_compare_and_swap

Add AO_GENERALIZE_ASM_BOOL_CAS new macro to allow AO_compare_and_swap
definition via AO_fetch_compare_and_swap instead of own ASM-based one

* src/atomic_ops/sysdeps/armcc/arm_v6.h (AO_compare_and_swap): Do not
define if AO_GENERALIZE_ASM_BOOL_CAS.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_compare_and_swap): Likewise.
* src/atomic_ops/sysdeps/gcc/hexagon.h (AO_compare_and_swap):
Likewise.
* src/atomic_ops/sysdeps/gcc/powerpc.h (AO_compare_and_swap,
AO_compare_and_swap_acquire, AO_compare_and_swap_release,
AO_compare_and_swap_full): Likewise.
* src/atomic_ops/sysdeps/gcc/x86.h (AO_compare_and_swap_full):
Likewise.
* src/atomic_ops/sysdeps/gcc/x86_64.h (AO_compare_and_swap_full):
Likewise.
* src/atomic_ops/sysdeps/sunc/x86.h (AO_compare_and_swap_full):
Likewise.
* src/atomic_ops/sysdeps/sunc/x86_64.h (AO_compare_and_swap_full):
Likewise.