QmakePM: Find prf files for CONFIG values

... in the pro file editor.
When the user selects "Jump to file under cursor" (e.g. via F2), and the
string under the cursor is not resolvable as a local file path, we
assume it is a CONFIG value and try to locate a corresponding prf file.
To this end, we expose the "feature roots" information of the qmake
evaluator in the QmakeProFile class.

Fixes: QTCREATORBUG-15753
Change-Id: Ibdc6e194a40f07030a5d21f2ddc7b92b63d1765b
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp

@@ -1616,6 +1616,7 @@ void QmakeProFile::applyEvaluate(QmakeEvalResult *evalResult)
             m_varValues = result->newVarValues;
 
         m_displayName = singleVariableValue(Variable::QmakeProjectName);
+        m_featureRoots = m_readerExact->featureRoots();
     } // result == EvalOk
 
     if (!result->directoriesWithWildcards.isEmpty()) {