Problem: one more test fails on GNU/Hurd

Solution: mark test_rebind_ipc as XFAIL on Hurd as it does not
implement getsockname on IPC and thus it's impossible to use
wildcard IPC binds.
Document that ZMQ_LAST_ENDPOINT does not work on Hurd with IPC.

Makefile.am

@@ -1044,10 +1044,13 @@ if !ON_LINUX
 XFAIL_TESTS += tests/test_abstract_ipc
 endif
 
+#  GNU/Hurd does not support getsockname on IPC, so ZMQ_LAST_ENDPOINT cannot be
+#  used with IPC, so the following tests will fail
 if ON_GNU
 XFAIL_TESTS += tests/test_ipc_wildcard \
 		tests/test_reqrep_ipc \
 		tests/test_pair_ipc \
+		tests/test_rebind_ipc \
 		tests/test_term_endpoint
 endif
 

doc/zmq_getsockopt.txt

@@ -370,6 +370,7 @@ The 'ZMQ_LAST_ENDPOINT' option shall retrieve the last endpoint bound for
 TCP and IPC transports. The returned value will be a string in the form of
 a ZMQ DSN. Note that if the TCP host is INADDR_ANY, indicated by a *, then
 the returned address will be 0.0.0.0 (for IPv4).
+Note: not supported on GNU/Hurd with IPC due to non-working getsockname().
 
 [horizontal]
 Option value type:: NULL-terminated character string