Index: runtimes/CMakeLists.txt
===================================================================
--- runtimes/CMakeLists.txt
+++ runtimes/CMakeLists.txt
@@ -186,6 +186,7 @@
                              # Builtins were built separately above
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
+                                        -DLLVM_MAIN_SRC_DIR=${LLVM_MAIN_SRC_DIR}
                              PASSTHROUGH_PREFIXES ${prefixes}
                              EXTRA_TARGETS ${extra_targets}
                                             ${test_targets}