Upgrade openssh to v9.1

[dscho]

This is a work-in-progress, mainly because I want to upgrade libfido2, too, in order to get ssh-keygen -t ecdsa-sk to use Windows Hello, but in my current attempts to build it, things break like this:

$ ssh-keygen.exe -v -v -v -v -v -v -t ecdsa-sk
Generating public/private ecdsa-sk key pair.
You may need to touch your authenticator to authorize key generation.
debug3: start_helper: started pid=53312
debug3: ssh_msg_send: type 5
debug3: ssh_msg_recv entering
debug1: start_helper: starting /usr/lib/ssh/ssh-sk-helper
ssh_msg_recv: read header: Software caused connection abort
client_converse: receive: unexpected internal error
debug3: reap_helper: pid=53312
reap_helper: helper exited with non-zero exit status
Key enrollment failed: unexpected internal error

This addresses git-for-windows/git#4051

[dscho]

I've decided to let the libfido2 upgrade slide for a while, as I suspect it to be quite a bit involved due to the segmentation fault (the first time I tried to get libfido2 to build and work properly, it took a couple of days to get it right, that's an amount of time I cannot spare right now).

[dscho]

Now off to the races: build libcbor first.

[dscho]

And now libfido2.

[dscho]

And now libfido2.

Which failed because of a missing public key. I edited the Azure Pipeline definition and started another build.

[dscho]

And now, finally, let's build openssh.

[dscho]

It finally built all right!