Utilities/Sphinx: Add CMake_OPTIONAL_COMPONENT macro

When building this directory independently define the macro since we
will not get the definition from the top level of the source tree.

Utilities/Sphinx/CMakeLists.txt

@@ -19,6 +19,9 @@ if(NOT CMake_SOURCE_DIR)
   include(${CMake_SOURCE_DIR}/Source/CMakeInstallDestinations.cmake)
   unset(CMAKE_DATA_DIR)
   unset(CMAKE_DATA_DIR CACHE)
+  macro(CMake_OPTIONAL_COMPONENT)
+    set(COMPONENT "")
+  endmacro()
 endif()
 project(CMakeHelp NONE)