message: Add missing sys_setitimer() syscall to syscall.h.
diff: @@ -55,6 +55,9 @@ extern "C" {
  #endif
  /* Opaque structures (may point to Rust structures or be used to not clash with types defined by the C library) */
  +struct _HermitItimerval;
  +typedef struct _HermitItimerval HermitItimerval;
  +
  struct _HermitRecursiveMutex;
  typedef struct _HermitRecursiveMutex HermitRecursiveMutex;
  @@ -139,6 +142,7 @@ int sys_gettimeofday(HermitTimeval* tp, void* tz);
  unsigned int sys_get_number_of_processors(void);
  unsigned short sys_get_processor_frequency(void);
  off_t sys_lseek(int fd, off_t offset, int whence);
  +int sys_setitimer(int which, const HermitItimerval* value, HermitItimerval* ovalue);
  void sys_yield(void);
  int sys_kill(tid_t dest, int signum);
  int sys_signal(signal_handler_t handler);
  