Rather than defining _WIN32_WINNT only in a handful of files, define
it in config.h, like we do with _GNU_SOURCE.
(Also remove a "#define WIN32_LEAN_AND_MEAN" that isn't really all
that useful.)
https://bugzilla.gnome.org/show_bug.cgi?id=688109
-glib/gmarkup.c: Use G_VA_COPY() instead of va_copy() as va_copy() may not
be universally available.
-gio/gtestdbus.c: Include io.h on Windows for close()
Using GIO here may cause the gvfs module to be loaded, which
in turn gets onto the session bus to talk to gvfsd - not ideal
if you are trying to control the session bus life cycle. Instead,
just use old-fashioned glib file utils.
-gconverterinputstream.c: Avoid GCCism by not using non-standard pointer
arithmetic on void*, but do a cast to char * as that seems to be what the
variable was used for.
-gtestdbus.c: Don't include unistd.h unconditionally, and use g_usleep()
instead of usleep(), as usleep() is not universally available.
