fix errno behavior in clock_* functions

these functions are specified inconsistent in whether they're
specified to return an error value, or return -1 and set errno.
hopefully now they all match what POSIX requires.

src/time/clock_getres.c

@@ -1,4 +1,3 @@
-#define SYSCALL_RETURN_ERRNO
 #include <time.h>
 #include "syscall.h"
 

src/time/clock_gettime.c

@@ -1,4 +1,3 @@
-#define SYSCALL_RETURN_ERRNO
 #include <time.h>
 #include "syscall.h"
 

src/time/clock_settime.c

@@ -1,4 +1,3 @@
-#define SYSCALL_RETURN_ERRNO
 #include <time.h>
 #include "syscall.h"