mach: Add missing assert.h include

sysdeps/mach/clock_gettime.c

@@ -18,6 +18,7 @@
 #include <errno.h>
 #include <time.h>
 #include <mach.h>
+#include <assert.h>
 #include <shlib-compat.h>
 
 /* Get the current time of day, putting it into *TS.
@@ -31,6 +32,7 @@ __clock_gettime (clockid_t clock_id, struct timespec *ts)
   switch (clock_id) {
 
     case CLOCK_REALTIME:
+    case CLOCK_MONOTONIC:
       {
 	/* __host_get_time can only fail if passed an invalid host_t.
 	   __mach_host_self could theoretically fail (producing an