Add PlowShowTime prototype when NO_RUSAGE isn't defined

While there, change function's type from (implicit) int to void.

plow/PlowMain.c

@@ -2249,6 +2249,7 @@ plowYankCreate()
 }
 
 #ifndef	NO_RUSAGE
+void
 plowShowTime(t1, t2, nqueued, nprocessed, nmoved)
     struct rusage *t1, *t2;
     int nqueued, nprocessed, nmoved;

plow/plowInt.h

@@ -280,6 +280,10 @@ extern void plowTechShow();
 extern void plowUpdateLabels();
 extern void plowYankCreate();
 
+#ifndef NO_RUSAGE
+extern void plowShowTime();
+#endif
+
 /* ------------------------- Debugging flags -------------------------- */
 
 /*