openssh: fix +fido2 variant

[iay]

Closes: https://trac.macports.org/ticket/62890

Description

Allows the +fido2 variant of openssh to compile so that it can be used with security keys.

Does not bring the port up to date with upstream as that would require the patch for the +gsskex variant to be updated.

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 11.3.1 20E241 x86_64
Xcode 12.5 12E262

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?
• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?

Existing tests do not run on my system either before or after this patch. I believe the issue to be something to do with the sandboxing of the sshd instance fired up during testing. It's possible this is macOS version specific.

I have tested ssh itself, the security key functionality in particular, and ssh-add. Other binaries at least fire up and give their versions.