Fix compiling with XCode 4.3

XCode 4.3 moved the location of the SDK dir, so change the qmake
test to not use the old hardcoded location. Also change the test
to look for versions before 10.6 instead of later than 10.6 so 10.8+
gets detected correctly.

Change-Id: I1cb53a18c4b4f484d0d9de9c9d5e9641018f2502
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>

src/plugins/bearer/corewlan/corewlan.pro

@@ -5,7 +5,7 @@ QT = core-private network-private
 LIBS += -framework Foundation -framework SystemConfiguration
 
 contains(QT_CONFIG, corewlan) {
-    isEmpty(QMAKE_MAC_SDK)|contains(QMAKE_MAC_SDK, "/Developer/SDKs/MacOSX10\.[67]\.sdk") {
+    !contains(QMAKE_MAC_SDK, ".*MacOSX10\\.[345]\\.sdk") {
          LIBS += -framework CoreWLAN -framework Security
     }
 }