qt_common.prf: when looking for GCC >= 4.6, match GCC 6+, too

Change-Id: Ia04690f62faa214fb91dffc758e253b5a64e5648
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

mkspecs/features/qt_common.prf

@@ -69,9 +69,9 @@ warnings_are_errors:warning_clean {
             QMAKE_CXXFLAGS_WARN_ON += -Werror -ww177,1224,1478,1881 $$WERROR
         }
     } else:gcc:!clang:!intel_icc {
-        # GCC 4.6-4.9, 5.x
+        # GCC 4.6-4.9, 5.x, ...
         ver = $${QT_GCC_MAJOR_VERSION}.$${QT_GCC_MINOR_VERSION}
-        contains(ver, "(4\\.[6789]|5\\..)") {
+        contains(ver, "(4\\.[6789]|[5-9]\\..)") {
             QMAKE_CXXFLAGS_WARN_ON += -Werror -Wno-error=cpp -Wno-error=deprecated-declarations $$WERROR
 
             # GCC prints this bogus warning, after it has inlined a lot of code