ClangTools: Avoid horizontal scrolling in the diagnostics view

Also, show the diagnostic text in the tooltip because the text might be
elided in the view now.

Change-Id: I7f38acacf72d68d7e4b696a01c7a0d1a76b4ed98
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangtools/clangtoolsdiagnosticview.cpp

@@ -34,6 +34,7 @@
 
 #include <QAction>
 #include <QDebug>
+#include <QHeaderView>
 
 using namespace Debugger;
 
@@ -103,5 +104,12 @@ bool DiagnosticView::eventFilter(QObject *watched, QEvent *event)
     }
 }
 
+void DiagnosticView::setModel(QAbstractItemModel *model)
+{
+    Debugger::DetailedErrorView::setModel(model);
+    header()->setStretchLastSection(false);
+    header()->setSectionResizeMode(0, QHeaderView::Stretch);
+}
+
 } // namespace Internal
 } // namespace ClangTools