On Windows, gpgme expects gpgme-w32spawn.exe to be in the same directory as the current
process executable. This assumption might be wrong, e.g., for bundled python, which is
in instdir/program/python-core-x.y.z/bin, while gpgme-w32spawn.exe is in instdir/program.
In this case, if an operation in a python script requires initializing gpgme, it will be
interrupted by a modal warning box telling that gpgme-w32spawn.exe was not found.

If we can't find gpgme-w32spawn.exe in the current executable location, then try to find
the spawn executable, and inform gpgme about actual location using gpgme_set_global_flag.

Change-Id: Ie30a0d4a6666767e8c54f1bdc67b67570d6ea47a
Reviewed-on: https://gerrit.libreoffice.org/71014
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>