Build cling-demo as part of cling.

interpreter/cling/tools/CMakeLists.txt

@@ -12,4 +12,5 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/../lib/UserInterface/textinput
   add_subdirectory(driver)
   add_subdirectory(Jupyter)
   add_subdirectory(libcling)
+  add_subdirectory(demo)
 endif()

interpreter/cling/tools/demo/CMakeLists.txt

@@ -8,18 +8,24 @@
 
 cmake_minimum_required(VERSION 3.5)
 
+# Cling needs at least C++11; so does this demo.
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-project(cling-demo)
+if (CMAKE_PROJECT_NAME)
+  # Building as part of cling; all CMake variables are set.
+else()
+  # Building as separate project.
+  project(cling-demo)
 
-# This project needs cling.
-find_package(cling REQUIRED)
+  # This project needs cling.
+  find_package(cling REQUIRED)
+endif()
 
-# It has one binary:
+# The project has one binary:
 add_executable(cling-demo cling-demo.cpp)
 
-# ...which links against clingInterpreter and its dependencies.
+# ...which links against clingInterpreter (and its dependencies).
 target_link_libraries(cling-demo clingInterpreter)
 
 # Provide LLVMDIR to cling-demp.cpp: