Don't build tex2rtf and HelpGen utils in non-GUI buildbot builds.

Both of those are obsolete and don't exist in 2.9 any longer.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74512 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't use wxCriticalSection in wxWakeUpPipeMT if wxUSE_THREADS==0.

In fact, don't define wxWakeUpPipeMT class at all when not using threads.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74513 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775