The es_poll API is not supported under Windows. However, we need this to be
abale to release GnuPG 2.2.
We can take the code from gpgme and put this into libgpg-error. I would suggest
to add a mode keyword "pollable" to es_fopen et all which will be a NOP under
Unix but under Windows uses the GPGME I/O stuff for that file.
In the long run we should repalce that code by async I/O using the code we have
in GpgOL. But right now that would delay things too much due to that bretty