CMake: Reference test targets only when BUILD_TESTING is ON

You cannot set a property on a target that's not there, and
these targets are not there when BUILD_TESTING is OFF.

Thanks to Sankhesh Jhaveri for the bug report.

CMakeLists.txt

@@ -231,11 +231,13 @@ MACRO (CMAKE_BUILD_UTILITIES)
   CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}_c "${kwsys_folder}")
   CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}EncodeExecutable "${kwsys_folder}")
   CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}ProcessFwd9x "${kwsys_folder}")
-  CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestDynload "${kwsys_folder}")
-  CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestProcess "${kwsys_folder}")
-  CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestsC "${kwsys_folder}")
-  CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestsCxx "${kwsys_folder}")
-  CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestSharedForward "${kwsys_folder}")
+  if(BUILD_TESTING)
+    CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestDynload "${kwsys_folder}")
+    CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestProcess "${kwsys_folder}")
+    CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestsC "${kwsys_folder}")
+    CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestsCxx "${kwsys_folder}")
+    CMAKE_SET_TARGET_FOLDER(${KWSYS_NAMESPACE}TestSharedForward "${kwsys_folder}")
+  endif()
 
   #---------------------------------------------------------------------
   # Setup third-party libraries.
@@ -598,7 +600,9 @@ ADD_SUBDIRECTORY(Source)
 ADD_SUBDIRECTORY(Utilities)
 ADD_SUBDIRECTORY(Tests)
 
-CMAKE_SET_TARGET_FOLDER(CMakeLibTests "Tests")
+if(BUILD_TESTING)
+  CMAKE_SET_TARGET_FOLDER(CMakeLibTests "Tests")
+endif()
 CMAKE_SET_TARGET_FOLDER(cmw9xcom "Utilities/Win9xCompat")
 CMAKE_SET_TARGET_FOLDER(documentation "Documentation")