[libc++] Move _LIBCPP_NO_THREAD_SAFETY_ANALYSIS to __config

This makes __threading_support contain nothing but the base threading
API provided by the system.

Differential Revision: https://reviews.llvm.org/D155458

Author: ldionne

libcxx/include/__config

@@ -1137,6 +1137,12 @@ __sanitizer_verify_double_ended_contiguous_container(const void*, const void*, c
 #    define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
 #  endif
 
+#  if defined(__FreeBSD__) && defined(__clang__) && __has_attribute(__no_thread_safety_analysis__)
+#    define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS __attribute__((__no_thread_safety_analysis__))
+#  else
+#    define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS
+#  endif
+
 #  if defined(_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS)
 #    if defined(__clang__) && __has_attribute(acquire_capability)
 // Work around the attribute handling in clang.  When both __declspec and

libcxx/include/__threading_support

@@ -42,12 +42,6 @@
 #define _LIBCPP_THREAD_ABI_VISIBILITY inline _LIBCPP_INLINE_VISIBILITY
 #endif
 
-#if defined(__FreeBSD__) && defined(__clang__) && __has_attribute(no_thread_safety_analysis)
-#define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS __attribute__((no_thread_safety_analysis))
-#else
-#define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS
-#endif
-
 typedef ::timespec __libcpp_timespec_t;
 #endif // !defined(_LIBCPP_HAS_NO_THREADS)