Profiler improvements: more-accurate timers, overflow checks.
* profiler.c: Don't include stdio.h, limits.h, sys/time.h, signal.h, setjmp.h. Include systime.h instead. (saturated_add): New function. (record_backtrace, current_sample_interval): Use EMACS_INT, not size_t. (record_backtrace, handle_profiler_signal): Saturate on fixnum overflow. (profiler_timer, profiler_timer_ok) [HAVE_TIMER_SETTIME]: New static vars. (enum profiler_cpu_running): New enumn. (profiler_cpu_running): Now of that enum type, not bool. All uses changed to store the new value. (handle_profiler_signal): Rename from sigprof_handler_1, for consistency with other handlers. Do not check whether cpu_log is a hash-table if garbage collecting, since it doesn't matter in that case. (deliver_profiler_signal): Rename from sigprof_handler, for consistency with other handlers. (setup_cpu_timer): New function, with much of what used to be in Fprofiler_cpu_start. Check for out-of-range argument. Prefer timer_settime if available, and prefer thread cputime clocks, then process cputime clocks, then monotonic clocks, to the old realtime clock. Use make_timeval to round more-correctly when falling back to setitimer. (Fprofiler_cpu_start): Use it. (Fprofiler_cpu_stop): Prefer timer_settime if available. Don't assume that passing NULL as the 2nd argument of setitimer is the same as passing a pointer to all-zero storage. Ignore SIGPROF afterwards. (malloc_probe): Saturate at MOST_POSITIVE_FIXNUM. * sysdep.c (emacs_sigaction_init): Also mask out SIGPROF in non-fatal signal handlers. Ignore SIGPROF on startup. * syssignal.h (PROFILER_CPU_SUPPORT): Define this macro here, not in profiler.c, since sysdep.c now uses it.
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