Fix compilation issue with clang.

cppeditor.cpp:2631:13: error: use of overloaded operator '+' is ambiguous (with operand types 'QChar' and 'QChar')
            + characterAt(pos - 2)
            ^ ~~~~~~~~~~~~~~~~~~~~
../../../../../builds/qt5-stable/qtbase/include/QtCore/../../src/corelib/tools/qstring.h:1116:22: note: candidate function
inline const QString operator+(const QString &s1, QChar s2)
                     ^
../../../../../builds/qt5-stable/qtbase/include/QtCore/../../src/corelib/tools/qstring.h:1118:22: note: candidate function
inline const QString operator+(QChar s1, const QString &s2)
                     ^
../../../../../builds/qt5-stable/qtbase/include/QtCore/../../src/corelib/tools/qstring.h:1114:22: note: candidate function
inline const QString operator+(const QString &s1, const QString &s2)
                     ^

Change-Id: I65663a901d301d6b0a3df2c8b5631e9aa5ab081b
Reviewed-by: David Schulz <david.schulz@digia.com>

src/plugins/cppeditor/cppeditor.cpp

@@ -485,7 +485,7 @@ DoxygenGenerator::DocumentationStyle doxygenStyle(const QTextCursor &cursor,
 {
     const int pos = cursor.position();
 
-    QString comment = doc->characterAt(pos - 3)
+    QString comment = QString(doc->characterAt(pos - 3))
             + doc->characterAt(pos - 2)
             + doc->characterAt(pos - 1);
 
@@ -2627,7 +2627,7 @@ bool CPPEditorWidget::handleDocumentationComment(QKeyEvent *e)
 bool CPPEditorWidget::isStartOfDoxygenComment(const QTextCursor &cursor) const
 {
     const int pos = cursor.position();
-    QString comment = characterAt(pos - 3)
+    QString comment = QString(characterAt(pos - 3))
             + characterAt(pos - 2)
             + characterAt(pos - 1);