diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -5,6 +5,8 @@
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(Clang)
   set(CLANG_BUILT_STANDALONE TRUE)
+  message(WARNING "The Standalone build is deprecated in this release. Please
+    use -DLLVM_ENABLE_PROJECTS='...;clang;...' to build clang.")
 endif()
 
 # Must go below project(..)