Index: llvm/trunk/docs/CMake.rst
===================================================================
--- llvm/trunk/docs/CMake.rst
+++ llvm/trunk/docs/CMake.rst
@@ -339,6 +339,14 @@
   will not be used.  If the variable for an external project does not point
   to a valid path, then that project will not be built.
 
+**LLVM_EXTERNAL_PROJECTS**:STRING
+  Semicolon-separated list of additional external projects to build as part of
+  llvm. For each project LLVM_EXTERNAL_<NAME>_SOURCE_DIR have to be specified
+  with the path for the source code of the project. Example:
+  ``-DLLVM_EXTERNAL_PROJECTS="Foo;Bar"
+    -DLLVM_EXTERNAL_FOO_SOURCE_DIR=/src/foo
+    -DLLVM_EXTERNAL_BAR_SOURCE_DIR=/src/bar``.
+
 **LLVM_USE_OPROFILE**:BOOL
   Enable building OProfile JIT support. Defaults to OFF.
 
Index: llvm/trunk/tools/CMakeLists.txt
===================================================================
--- llvm/trunk/tools/CMakeLists.txt
+++ llvm/trunk/tools/CMakeLists.txt
@@ -50,4 +50,9 @@
 # file as external projects.
 add_llvm_implicit_projects()
 
+# Add subprojects specified using LLVM_EXTERNAL_PROJECTS
+foreach(p ${LLVM_EXTERNAL_PROJECTS})
+  add_llvm_external_project(${p})
+endforeach(p)
+
 set(LLVM_COMMON_DEPENDS ${LLVM_COMMON_DEPENDS} PARENT_SCOPE)