Enable macro editing for the Clang indexer

Refactor much of the code from Environment* classes to NameValue* classes
to share it with the preprocessor macro settings.

Change-Id: Ica4ee817aa338230c422b30d91240d266248d226
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qnx/qnxqtversion.cpp

@@ -184,7 +184,7 @@ void QnxQtVersion::updateEnvironment() const
     }
 }
 
-QList<Utils::EnvironmentItem> QnxQtVersion::environment() const
+Utils::EnvironmentItems QnxQtVersion::environment() const
 {
     return QnxUtils::qnxEnvironment(sdpPath());
 }