Use a separate build flag to enable gssapi
In !720 (merged), compiling gitlab-sshd
with CGO_ENABLED=0
disables gssapi
.
However, there might be reasons to keep cgo and disable gssapi. For example, DNS resolution works differently if cgo is enabled (https://pkg.go.dev/net#hdr-Name_Resolution).
We probably want to consider using another build flag.
This came out of gitlab!113079 (comment 1297443155).