Explain why clock(3) isn't broken.

Bug: 17441123
Change-Id: I6ee9b7f54bab55b1a8760ce9bcaaa6eab1dcc492

libc/bionic/clock.cpp

@@ -34,5 +34,8 @@
 clock_t clock() {
   tms t;
   times(&t);
+  // Although times(2) and clock(3) both use the type clock_t, the units are
+  // different. For times(2) it's pure clock ticks, but for clock(3) the unit
+  // is CLOCKS_PER_SEC, so we need to scale appropriately.
   return (t.tms_utime + t.tms_stime) * (CLOCKS_PER_SEC / sysconf(_SC_CLK_TCK));
 }