Steal GCC's --time-report support.

* lib/timevar.c, lib/timevar.h, lib/timevar.def: New,
stolen/adjusted from GCC.
* m4/stage.m4: Remove time related checks.
* m4/timevar.m4: New.
* configure.in: Adjust.
* src/system.h: Adjust to using timevar.h.
* src/getargs.h, src/getargs.c: Support trace_time for
--trace=time.
* src/main.c (stage): Remove.
(main): Replace `stage' invocations with timevar calls.
* src/output.c: Insert pertinent timevar calls.

src/system.h

@@ -110,10 +110,12 @@ char *xstrndup PARAMS ((const char *s, size_t n));
 #endif
 
 
-/* Find `times' where available.  */
-#if HAVE_SYS_TIMES_H
-# include <sys/times.h>
-#endif
+/*----------------.
+| Using timevar.  |
+`----------------*/
+
+#include "timevar.h"
+extern int time_report;
 
 
 /*---------------------.