debugger: replace hack to select trk adapter and pass parameters by a new one

Now .pro files can be used as project description as usual. To make the
debugger pick up the "on device" part a magic commandline is needed:
"@sym@ c:\sys\bin\your.exe  /path/to/your.sym"

If the project is not compilable, remove the Make and QMake buildsteps
and add a new Custom step that's only calling /bin/true.

src/plugins/debugger/gdb/gdbengine.cpp

@@ -1475,7 +1475,7 @@ AbstractGdbAdapter *GdbEngine::determineAdapter(const DebuggerStartParametersPtr
         break;
     }
     // @todo: remove testing hack
-    if (sp->executable.endsWith(_(".sym")))
+    if (sp->processArgs.at(0) == _("@sym@"))
         return m_trkAdapter;
     switch (sp->startMode) {
     case AttachCore: