Make q2c link under mingw32, by eliminating the dependency on

Make q2c link under mingw32, by eliminating the dependency on
localtime.  Gnulib replaces localtime by a fixed version, but we don't
link q2c against gnulib.  q2c only uses localtime to put the time of
processing into the output file, which I've never in practice found to
be useful, so the patch just drops this feature.

Patch #5740.