I used regedit (run as administrator) to change the Windows services to run c:\cygwin64\bin\cygrunsrv.exe and sshd restarted effortlessly in 64 bits. samples/exifprint.cpp compiles/links/runs as documented. Very pleased.
I still haven't persuaded cygwin to link correctly. Something horribly wrong. I've realised that the buildserver sshd is 32 bit and therefore builds a 32 bit library. I might attempt the configure sshd to run cygwin64, however it took a lot of effort to get everything to build over sshd, I'm reluctant to modify anything about sshd. I'll feel differently when I work on this tomorrow.
Robin Mills