Use the realtime clock for the monotonic clock. This is of course not a proper
implementation (which is being done in Mach), but will permit to fix at least
the iceweasel stack.

vlc however doesn't build when _POSIX_CLOCK_SELECTION is enabled but
_POSIX_TIMERS is not, and they refuse to fix that (see #765578), so disable the
former.

---
 sysdeps/mach/hurd/bits/posix_opt.h |    2 +-
 sysdeps/unix/clock_gettime.c       |    1 +
 2 files changed, 2 insertions(+), 1 deletion(-)
Index: glibc-2.27/sysdeps/mach/clock_gettime.c
===================================================================
--- glibc-2.27.orig/sysdeps/mach/clock_gettime.c
+++ glibc-2.27/sysdeps/mach/clock_gettime.c
@@ -48,7 +48,7 @@ timer_create (clockid_t clock_id, struct
 int
 __clock_gettime (clockid_t clock_id, struct timespec *ts)
 {
-  if (clock_id != CLOCK_REALTIME)
+  if (clock_id != CLOCK_REALTIME && clock_id != CLOCK_MONOTONIC)
     {
       errno = EINVAL;
       return -1;
Index: glibc-2.27/sysdeps/pthread/timer_create.c
===================================================================
--- glibc-2.27.orig/sysdeps/pthread/timer_create.c
+++ glibc-2.27/sysdeps/pthread/timer_create.c
@@ -48,7 +48,7 @@ timer_create (clockid_t clock_id, struct
       return -1;
     }
 
-  if (clock_id != CLOCK_REALTIME)
+  if (clock_id != CLOCK_REALTIME && clock_id != CLOCK_MONOTONIC)
     {
       __set_errno (EINVAL);
       return -1;
Index: glibc-2.27/sysdeps/mach/hurd/bits/posix_opt.h
===================================================================
--- glibc-2.27.orig/sysdeps/mach/hurd/bits/posix_opt.h
+++ glibc-2.27/sysdeps/mach/hurd/bits/posix_opt.h
@@ -163,10 +163,10 @@
 #define _POSIX_THREAD_PROCESS_SHARED	-1
 
 /* The monotonic clock might be available.  */
-#define _POSIX_MONOTONIC_CLOCK	0
+#define _POSIX_MONOTONIC_CLOCK	200809L
 
-/* The clock selection interfaces are available.  */
-#define _POSIX_CLOCK_SELECTION	200809L
+/* The clock selection interfaces are not really available yet.  */
+#define _POSIX_CLOCK_SELECTION	-1
 
 /* Advisory information interfaces could be available in future.  */
 #define _POSIX_ADVISORY_INFO	0