Index: libcxx/cmake/caches/Build-ext-thread-lib.cmake
===================================================================
--- /dev/null
+++ libcxx/cmake/caches/Build-ext-thread-lib.cmake
@@ -0,0 +1,2 @@
+set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
+set(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY ON CACHE BOOL "")