per-thread msgbox for SHOW_RESULTS in samples on Windows is annoying

Maybe having one or two msgboxs for the samples/ clients, which are just
intended for demonstrations and meant to be modified and rebuilt, is ok and
worth the sacrifice to ensure there's output for graphical apps -- but a
msgbox per thread just gets annoying, for the memtrace and other samples.

Start by locating the SHOW_RESULTS handling in the samples/ clients, especially the memtrace and other samples mentioned in the issue. Trace how output is shown for graphical applications on Windows and identify where message boxes are created per thread. Done means samples retain visible output while avoiding a message box for every thread.

Written by the indexing model from the issue text.