Don't disable C++11 on Mac OS X

On OS X, enabling C++11 has the side effect of switching
the standard library from libstdc++ to libc++. Qt 5.2
enables C++11 by default, which leads to a Qt build
that uses both standard libraries. This is something
we would like to avoid.

Change-Id: I0ad8fb550ef79ac37ac97a75799ac38aa19d39d4
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/script/script.pro

@@ -76,7 +76,9 @@ integrity {
 }
 
 # WebKit doesn't compile in C++0x mode
-*-g++*:QMAKE_CXXFLAGS -= -std=c++0x -std=gnu++0x
-CONFIG -= c++11
+!mac {
+    *-g++*:QMAKE_CXXFLAGS -= -std=c++0x -std=gnu++0x
+    CONFIG -= c++11
+}
 
 TR_EXCLUDE = $$WEBKITDIR/*