Resubmit "Fix llvm-lit script generation in libcxx."

After speaking with the libcxx owners, they agreed that this is
a bug in the bot that needs to be fixed by the bot owners, and
the CMake changes are correct.

llvm-svn: 313643
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index e402dae..f2b7f83 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -653,6 +653,7 @@
 #
 # However, since some submission systems strip test/ subdirectories, check for
 # it before adding it.
+
 if(IS_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/test")
   add_subdirectory(test)
 endif()
@@ -660,6 +661,15 @@
   add_subdirectory(lib/abi)
 endif()
 
+if (LIBCXX_STANDALONE_BUILD AND EXISTS "${LLVM_MAIN_SRC_DIR}/utils/llvm-lit")
+  # Make sure the llvm-lit script is generated into the bin directory, and do
+  # it after adding all tests, since the generated script will only work
+  # correctly discovered tests against test locations from the source tree that
+  # have already been discovered.
+  add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/llvm-lit
+                   ${CMAKE_CURRENT_BINARY_DIR}/llvm-lit)
+endif()
+
 if (LIBCXX_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()