libguestfs has used double and triple underscores in identifiers.
These aren't valid for global names in C++.
The first step is to replace all guestfs___* (3 underscores) with
guestfs_int_*. We've used guestfs_int_* elsewhere already as a prefix
for internal identifiers.
This is an entirely mechanical change done using:
git ls-files | xargs perl -pi.bak -e 's/guestfs___/guestfs_int_/g'
Reference: http://stackoverflow.com/a/228797