Use double-word atomic intrinsics for recent Clang versions (gcc/x86.h)

Use double-word atomic intrinsics for recent Clang versions (gcc/x86.h)

Older clang versions have some bugs or limitations that prevent from
using double-word built-in atomic operations.

Note: even as of clang-4.0, there seems to be a bug in some
double-word built-in operation if Thread Sanitizer is used.

* src/atomic_ops/sysdeps/gcc/x86.h [AO_GCC_ATOMIC_TEST_AND_SET
&& __APPLE_CC__ && __x86_64__]
(AO_SKIPATOMIC_double_compare_and_swap_ANY): Do not define if
AO_CLANG_PREREQ(9, 0); update comment.
* src/atomic_ops/sysdeps/gcc/x86.h [AO_GCC_ATOMIC_TEST_AND_SET
&& !__APPLE_CC__ && __clang__ && !__x86_64__
&& !AO_PREFER_BUILTIN_ATOMICS && !__CYGWIN__]
(AO_SKIPATOMIC_double_compare_and_swap_ANY,
AO_SKIPATOMIC_DOUBLE_LOAD_STORE_ANY): Do not define if
AO_CLANG_PREREQ(5, 0); update comment.
* src/atomic_ops/sysdeps/gcc/x86.h [AO_GCC_ATOMIC_TEST_AND_SET
&& !__APPLE_CC__ && __clang__ && __x86_64__ && !__ILP32__
&& AO_ADDRESS_SANITIZER] (AO_SKIPATOMIC_double_compare_and_swap_ANY
AO_SKIPATOMIC_DOUBLE_LOAD_STORE_ANY): Do not define if
AO_CLANG_PREREQ(4, 0); update comment.