CA-38567: Fail Unixext calls with a proper Unix_error.
CA-38567: Fail Unixext calls with a proper Unix_error.

Signed-off-by: Daniel Stodden <05f14ed2a2851619d24030f51bb8d7a9bac70353@citrix.com>

djs55/forkexecd,johnelse/forkexecd,xapi-project/message-switch,xapi-project/message-switch,xapi-project/message-switch