OS X: Use OSX_DEVELOPER_ROOT for app search path (#13066)

Since commit 4693cf84 (Xcode: Detect new default locations of Xcode 4.3
bits and pieces) Darwin.cmake detects the developer application
directory instead of hard-coding /Developer.  Replace the hard-coded
path in CMAKE_SYSTEM_APPBUNDLE_PATH using the computed result.

Modules/Platform/Darwin.cmake

@@ -242,7 +242,7 @@ SET(CMAKE_FIND_APPBUNDLE FIRST)
 SET(CMAKE_SYSTEM_APPBUNDLE_PATH
   ~/Applications
   /Applications
-  /Developer/Applications)
+  ${OSX_DEVELOPER_ROOT}/Applications)
 
 INCLUDE(Platform/UnixPaths)
 LIST(APPEND CMAKE_SYSTEM_PREFIX_PATH