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/getargs.c

@@ -55,8 +55,9 @@ static const char * const trace_args[] =
   "automaton  - contruction of the automaton",
   "bitsets    - use of bitsets",
   "grammar    - reading, reducing of the grammar",
-  "resource   - time and memory (where available)",
+  "resource   - memory consumption (where available)",
   "sets       - grammar sets: firsts, nullable etc.",
+  "time       - time consumption",
   "tools      - m4 invocation and preserve the temporary file",
   "all        - all of the above",
   0
@@ -70,6 +71,7 @@ static const int trace_types[] =
   trace_grammar,
   trace_resource,
   trace_sets,
+  trace_time,
   trace_tools,
   trace_all
 };