Linux: Add a crash handler providing a backtrace for debug builds.

Use case: You're working with a debug version of Qt Creator and you're
interested in getting a backtrace displayed as soon as Qt Creator
crashes without searching for the core file, starting your debugger, ...

Once a 'serious signal' (currently SIGILL, SIGFPE, SIGSEGV, SIGBUS,
SIGPIPE) is delivered, a popup displays the following debug information:

 - Qt Creator version (same as in the about dialog)
 - Kernel version (uname -a)
 - GNU/Linux Distribution (/etc/lsb-release)
 - Backtrace (by gdb)

Please note that this crash handler is built and used only in debug mode
on GNU/Linux. It's solely meant as a convenience tool for the developer.

In contrast to the breakpad integration, this crash handler operates
'offline'. There is no network i/o involved.

Change-Id: Idcfb1bf1ad68942615ecfe0dffc0d03154455049
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>

src/app/main.cpp

@@ -29,6 +29,7 @@
 **************************************************************************/
 
 #include "qtsingleapplication.h"
+#include "../tools/qtcreatorcrashhandler/crashhandlersetup.h"
 
 #include <app/app_version.h>
 #include <extensionsystem/iplugin.h>
@@ -228,6 +229,8 @@ int main(int argc, char **argv)
     const int threadCount = QThreadPool::globalInstance()->maxThreadCount();
     QThreadPool::globalInstance()->setMaxThreadCount(qMax(4, 2 * threadCount));
 
+    setupCrashHandler(); // Display a backtrace once a serious signal is delivered.
+
 #ifdef ENABLE_QT_BREAKPAD
     QtSystemExceptionHandler systemExceptionHandler;
 #endif
@@ -432,5 +435,7 @@ int main(int argc, char **argv)
         QTimer::singleShot(100, &pluginManager, SLOT(startTests()));
 #endif
 
-    return app.exec();
+    const int r = app.exec();
+    cleanupCrashHandler();
+    return r;
 }