re-enable QT_USE_FAST_CONCATENATION

includes workaround for breakage with old g++

qtcreator.pri

@@ -90,7 +90,7 @@ LIBS += -L$$IDE_LIBRARY_PATH
 
 #DEFINES += QT_NO_CAST_FROM_ASCII
 DEFINES += QT_NO_CAST_TO_ASCII
-#DEFINES += QT_USE_FAST_OPERATOR_PLUS QT_USE_FAST_CONCATENATION
+DEFINES += QT_USE_FAST_OPERATOR_PLUS QT_USE_FAST_CONCATENATION
 
 unix {
     CONFIG(debug, debug|release):OBJECTS_DIR = $${OUT_PWD}/.obj/debug-shared

src/libs/qmljs/parser/qmljsgrammar_p.h

@@ -61,7 +61,7 @@ QT_BEGIN_NAMESPACE
 class QmlJSGrammar
 {
 public:
-  enum {
+  enum VariousConstants {
     EOF_SYMBOL = 0,
     REDUCE_HERE = 99,
     SHIFT_THERE = 98,