By the time we get to ComputeLocalClient, we've already done
NextAvailableClient → ReserveClientIds → DetermineClientCmd (assuming
we're built with #define CLIENTIDS), so we can look up the name of the
client process and refuse to treat ssh's X forwarding as if it were
local.

v2: (Michel Dänzer)
    * Only match "ssh" itself, not other executable names starting with
      that prefix.
    * Ignore executable path for the match.
v3: (Michel Dänzer)
    * Use GetClientCmdName (Mark Kettenis)
    * Perform check on Windows as well, but only ignore path on Cygwin
      (Martin Peres, Emil Velikov, Jon Turney)
v4: (Michel Dänzer)
    * Cut of any colon and whatever comes after it. (Adam Jackson)
    * Add bugzilla reference.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93261



Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
(cherry picked from commit adefbaee)