Make sure that libCIndex links as a C++ library

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@83331 91177308-0d34-0410-b5e6-96231b3b80d8

tools/CIndex/CMakeLists.txt

@@ -21,3 +21,7 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     INSTALL_NAME_DIR "@executable_path/../lib"
     )
 endif()
+
+set_target_properties(CIndex
+  PROPERTIES
+  LINKER_LANGUAGE CXX)