Compile with Qt 5 (QFontMetrics constructor explicit).

Change-Id: Idd695326b4b3e162e2b691b3df0a5a4bfbff2fe6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/plugins/valgrind/callgrindtextmark.cpp

@@ -80,10 +80,10 @@ void CallgrindTextMark::paint(QPainter *painter, const QRect &paintRect) const
 
     // decrease font size if paint rect is too small (very unlikely, but may happen)
     QFont font = painter->font();
-    QFontMetrics fm = font;
+    QFontMetrics fm = QFontMetrics(font);
     while (fm.boundingRect(text).width() > paintRect.width()) {
         font.setPointSize(font.pointSize() - 1);
-        fm = font;
+        fm = QFontMetrics(font);
     }
     painter->setFont(font);