Debugger: Use LD_PRELOAD to load debugging helper.

on UNIX. Either set the LD_PRELOAD environment variable
using a gdb command or have the TermGdbAdapter set the
variable for the debuggee. For the remote adapter,
switch on toolchain. dlopen() is a fallback for
platforms where it is not supported and attaching
to running processes. Fixes a crash with gdb 7.0
(and spurious gdb 6.8 crashes with dlopen()).
Reviewed-by: hjk <qtc-committer@nokia.com>

src/plugins/debugger/gdb/plaingdbadapter.cpp

@@ -58,6 +58,15 @@ PlainGdbAdapter::PlainGdbAdapter(GdbEngine *engine, QObject *parent)
         engine, SLOT(readDebugeeOutput(QByteArray)));
 }
 
+AbstractGdbAdapter::DumperHandling PlainGdbAdapter::dumperHandling() const
+{
+#ifdef Q_OS_WIN
+    return DumperLoadedByGdb;
+#else
+    return DumperLoadedByGdbPreload;
+#endif
+}
+
 void PlainGdbAdapter::startAdapter()
 {
     QTC_ASSERT(state() == EngineStarting, qDebug() << state());