oce: disable on i686-pc-mingw32

There are multiple bugs related to i686-pc-mingw32. They seem to be fixable
but I don't think they are worth fixing when i686-w64-mingw32 works just
fine.

If you are interested in fixing i686-pc-mingw32, by all means feel free to
do so!

Signed-off-by: Timothy Gu <timothygu99@gmail.com>