Use clock(3) instead of time(3) to compute elapsed cpu time.

Index: base/config.h
--- base/config.h.orig
+++ base/config.h
@@ -39,7 +39,7 @@
 /* #define HAVE_GETRUSAGE */
 
 /* define the following if your system has ANSI C:  clock and CLOCKS_PER_SEC */
-/* #define HAVE_CLOCK */
+#define HAVE_CLOCK
 
 /* define the following if your (nominally BSD) system provides the SYSV
    string functions:  strchr, strrchr, memcpy, and memset */