Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -166,6 +166,9 @@
 option(LIBCXX_HAS_EXTERNAL_THREAD_API
   "Build libc++ with an externalized threading API.
    This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON." OFF)
+option(LIBCXXABI_HAS_EXTERNAL_THREAD_API
+  "Build libc++abi with an externalized threading API.
+   This option may only be set to ON when LIBCXXABI_ENABLE_THREADS=ON." OFF)
 
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
@@ -218,14 +221,21 @@
                       " when LIBCXX_ENABLE_THREADS is also set to OFF.")
 endif()
 
-if(LIBCXX_HAS_PTHREAD_API AND NOT LIBCXX_ENABLE_THREADS)
-  message(FATAL_ERROR "LIBCXX_HAS_PTHREAD_API can only be set to ON"
-                      " when LIBCXX_ENABLE_THREADS is also set to ON.")
+if(NOT LIBCXX_ENABLE_THREADS)
+  if(LIBCXX_HAS_PTHREAD_API)
+    message(FATAL_ERROR "LIBCXX_HAS_PTHREAD_API can only be set to ON"
+                        " when LIBCXX_ENABLE_THREADS is also set to ON.")
+  endif()
+  if(LIBCXX_HAS_EXTERNAL_THREAD_API)
+    message(FATAL_ERROR "LIBCXX_HAS_EXTERNAL_THREAD_API can only be set to ON"
+                        " when LIBCXX_ENABLE_THREADS is also set to ON.")
+  endif()
 endif()
 
-if(LIBCXX_HAS_EXTERNAL_THREAD_API AND NOT LIBCXX_ENABLE_THREADS)
-  message(FATAL_ERROR "LIBCXX_HAS_EXTERNAL_THREAD_API can only be set to ON"
-                      " when LIBCXX_ENABLE_THREADS is also set to ON.")
+if(LIBCXX_HAS_PTHREAD_API AND LIBCXX_HAS_EXTERNAL_THREAD_API)
+  message(FATAL_ERROR "The options LIBCXX_HAS_EXTERNAL_THREAD_API"
+                      "and LIBCXX_HAS_PTHREAD_API cannot be both"
+                      "set to ON at the same time.")
 endif()
 
 # Ensure LLVM_USE_SANITIZER is not specified when LIBCXX_GENERATE_COVERAGE
Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -257,7 +257,7 @@
     PROPERTIES
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
-      OUTPUT_NAME   "c++external_threads"
+      OUTPUT_NAME   "cxx_external_threads"
   )
 endif()
 
Index: test/CMakeLists.txt
===================================================================
--- test/CMakeLists.txt
+++ test/CMakeLists.txt
@@ -35,6 +35,7 @@
 pythonize_bool(LIBCXX_HAS_ATOMIC_LIB)
 pythonize_bool(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
 pythonize_bool(LIBCXX_HAS_EXTERNAL_THREAD_API)
+pythonize_bool(LIBCXXABI_HAS_EXTERNAL_THREAD_API)
 
 # By default, for non-standalone builds, libcxx and libcxxabi share a library
 # directory.
@@ -56,17 +57,23 @@
   @ONLY)
 
 if (LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY)
-  set(experimental_dep cxx_experimental)
+  set(LIBCXX_TEST_DEPS cxx_experimental)
+else()
+  set(LIBCXX_TEST_DEPS "")
 endif()
 
 if (LIBCXX_HAS_EXTERNAL_THREAD_API)
-  set(external_threads_dep cxx_external_threads)
+  list(APPEND LIBCXX_TEST_DEPS "cxx_external_threads")
+endif()
+
+if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
+  list(APPEND LIBCXX_TEST_DEPS "cxxabi_external_threads")
 endif()
 
 add_lit_testsuite(check-cxx
   "Running libcxx tests"
   ${CMAKE_CURRENT_BINARY_DIR}
-  DEPENDS cxx ${experimental_dep} ${external_threads_dep})
+  DEPENDS cxx ${LIBCXX_TEST_DEPS})
 
 add_custom_target(check-libcxx DEPENDS check-cxx)
 
Index: test/libcxx/test/config.py
===================================================================
--- test/libcxx/test/config.py
+++ test/libcxx/test/config.py
@@ -571,10 +571,6 @@
                 self.cxx.link_flags += [abs_path]
             else:
                 self.cxx.link_flags += ['-lc++']
-        # This needs to come after -lc++ as we want its unresolved thread-api symbols
-        # to be picked up from this one.
-        if self.get_lit_bool('libcxx_external_thread_api', default=False):
-            self.cxx.link_flags += ['-lc++external_threads']
 
     def configure_link_flags_abi_library(self):
         cxx_abi = self.get_lit_conf('cxx_abi', 'libcxxabi')
@@ -603,6 +599,10 @@
                 'C++ ABI setting %s unsupported for tests' % cxx_abi)
 
     def configure_extra_library_flags(self):
+        if self.get_lit_bool('cxx_ext_threads', default=False):
+            self.cxx.link_flags += ['-lcxx_external_threads']
+        if self.get_lit_bool('cxxabi_ext_threads', default=False):
+            self.cxx.link_flags += ['-lcxxabi_external_threads']
         self.target_info.add_cxx_link_flags(self.cxx.link_flags)
 
     def configure_color_diagnostics(self):
Index: test/lit.site.cfg.in
===================================================================
--- test/lit.site.cfg.in
+++ test/lit.site.cfg.in
@@ -28,7 +28,8 @@
 config.use_libatomic            = "@LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@"
 
 config.libcxxabi_shared         = "@LIBCXXABI_ENABLE_SHARED@"
-config.libcxx_external_thread_api  = "@LIBCXX_HAS_EXTERNAL_THREAD_API@"
+config.cxx_ext_threads          = "@LIBCXX_HAS_EXTERNAL_THREAD_API@"
+config.cxxabi_ext_threads       = "@LIBCXXABI_HAS_EXTERNAL_THREAD_API@"
 
 # Let the main config do the real work.
 config.loaded_site_config = True