[libc++] Add explicit ABI annotations to functions from the block runtime declared in <__functional/function.h> (#140592)

Author: philnik777

libcxx/include/__functional/function.h

@@ -752,8 +752,9 @@ class __policy_func<_Rp(_ArgTypes...)> {
 
 #  if _LIBCPP_HAS_BLOCKS_RUNTIME
 
-extern "C" void* _Block_copy(const void*);
-extern "C" void _Block_release(const void*);
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
+_LIBCPP_EXPORTED_FROM_ABI extern "C" void* _Block_copy(const void*);
+_LIBCPP_EXPORTED_FROM_ABI extern "C" void _Block_release(const void*);
 
 template <class _Rp1, class... _ArgTypes1, class _Alloc, class _Rp, class... _ArgTypes>
 class __func<_Rp1 (^)(_ArgTypes1...), _Alloc, _Rp(_ArgTypes...)> : public __base<_Rp(_ArgTypes...)> {
@@ -826,6 +827,7 @@ class __func<_Rp1 (^)(_ArgTypes1...), _Alloc, _Rp(_ArgTypes...)> : public __base
   }
 #    endif // _LIBCPP_HAS_RTTI
 };
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
 #  endif // _LIBCPP_HAS_EXTENSION_BLOCKS