Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -333,6 +333,8 @@
                         " is also set to ON.")
   endif()
   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
+  # propgate no threads to libcxx, which uses a different flag
+  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
 endif()
 
 if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)