Add test for custom command with a genex referring to a target.

This test failed before d8a59ea4 (Port cmGeneratorExpression to
cmTarget from cmGeneratorTarget, 2012-10-27), and passes after.

Tests/IncludeDirectories/TargetIncludeDirectories/CMakeLists.txt

@@ -45,3 +45,9 @@ set_property(TARGET TargetIncludeDirectories
   APPEND PROPERTY INCLUDE_DIRECTORIES
   "$<TARGET_PROPERTY:somelib::withcolons,INTERFACE_INCLUDE_DIRECTORIES>"
 )
+
+add_custom_target(test_custom_target
+        "some_bogus_custom_tool"
+        $<TARGET_PROPERTY:TargetIncludeDirectories,COMPILE_DEFINITIONS>
+        WORKING_DIRECTORY
+        "${CMAKE_CURRENT_SOURCE_DIR}")