C++: Support single quote digit separator in integer literals

C++14 supports the use of single quotes inserted between integer digits
as a separator.  Updates the built-in C++ code model to recognize such
quotes.  This fixes highlighting and indentation issues.

Change-Id: Ic35ce93060b96700a11d108dce1f3cf6c4543632
Fixes: QTCREATORBUG-14939
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/cplusplus/MatchingText.cpp

@@ -145,6 +145,7 @@ static LanguageFeatures languageFeatures()
     features.qtKeywordsEnabled = false;
     features.qtMocRunEnabled = false;
     features.cxx11Enabled = true;
+    features.cxx14Enabled = true;
     features.cxxEnabled = true;
     features.c99Enabled = true;
     features.objCEnabled = true;