diff --git a/libcxx/include/__threading_support b/libcxx/include/__threading_support
--- a/libcxx/include/__threading_support
+++ b/libcxx/include/__threading_support
@@ -282,7 +282,7 @@
   bool operator()(chrono::nanoseconds __elapsed) const;
 };
 
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_THREAD_ABI_VISIBILITY
 bool __libcpp_timed_backoff_policy::operator()(chrono::nanoseconds __elapsed) const
 {
     if(__elapsed > chrono::milliseconds(128))
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -323,7 +323,8 @@
 
 
 if (LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
-  file(GLOB LIBCXX_EXTERNAL_THREADING_SUPPORT_SOURCES ../test/support/external_threads.cpp)
+  set(LIBCXX_EXTERNAL_THREADING_SUPPORT_SOURCES
+      "${CMAKE_CURRENT_SOURCE_DIR}/../test/support/external_threads.cpp")
 
   if (LIBCXX_ENABLE_SHARED)
     add_library(cxx_external_threads SHARED ${LIBCXX_EXTERNAL_THREADING_SUPPORT_SOURCES})
@@ -337,6 +338,8 @@
       COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
       OUTPUT_NAME   "c++external_threads"
   )
+
+  target_link_libraries(cxx_external_threads PRIVATE cxx-headers)
 endif()
 
 if (LIBCXX_INSTALL_LIBRARY)