fix clock() function

it previously was returning the pseudo-monotonic-realtime clock
returned by times() rather than process cputime. it also violated C
namespace by pulling in times().

we now use clock_gettime() if available because times() has
ridiculously bad resolution. still provide a fallback for ancient
kernels without clock_gettime.

src/time/clock.c

 #include <time.h>
 #include <sys/times.h>
 
-/* this function assumes 100 hz linux and corrects for it */
+int __clock_gettime(clockid_t, struct timespec *);
+
 clock_t clock()
 {
+	struct timespec ts;
 	struct tms tms;
-	return (unsigned long)times(&tms)*10000;
+	if (!__clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))
+		return ts.tv_sec*1000000 + ts.tv_nsec/1000;
+	__syscall(SYS_times, &tms);
+	return (tms.tms_utime + tms.tms_stime)*100;
 }