Make build dependent on version of xcode, not version of OSX for DARWIN

indra/cmake/Variables.cmake

@@ -100,19 +100,19 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(DARWIN 1)
   
   execute_process(
-	COMMAND sh -c "sw_vers -productVersion | cut -d'.' -f1-2"
-	OUTPUT_VARIABLE DARWIN_VERSION )
+	COMMAND sh -c "xcodebuild -version | grep Xcode  | cut -d ' ' -f2 | cut -d'.' -f1-2"
+	OUTPUT_VARIABLE XCODE_VERSION )
 
   # To support a different SDK update these Xcode settings:
-  if (DARWIN_VERSION GREATER 10.6)
+  if (XCODE_VERSION GREATER 4.2)
   	set(CMAKE_OSX_DEPLOYMENT_TARGET 10.6)
 	set(CMAKE_OSX_SYSROOT macosx10.6)
 	set(CMAKE_XCODE_ATTRIBUTE_GCC_VERSION "com.apple.compilers.llvmgcc42")
-  else (DARWIN_VERSION GREATER 10.6)
+  else (XCODE_VERSION GREATER 4.2)
   	set(CMAKE_OSX_DEPLOYMENT_TARGET 10.5)
     set(CMAKE_OSX_SYSROOT /Developer/SDKs/MacOSX10.5.sdk)
   	set(CMAKE_XCODE_ATTRIBUTE_GCC_VERSION "4.0")
-  endif (DARWIN_VERSION GREATER 10.6)
+  endif (XCODE_VERSION GREATER 4.2)
       
   set(CMAKE_XCODE_ATTRIBUTE_DEBUG_INFORMATION_FORMAT dwarf-with-dsym)