gdb: rename async_init_signals to gdb_init_signals

The async_init_signals has, for some time, dealt with async and sync
signals, so removing the async prefix makes sense I think.

Additionally, as pointed out by Pedro:

  .....

The comments relating to SIGTRAP and SIGQUIT within this function are
out of date.

The comments for SIGTRAP talk about the signal disposition (SIG_IGN)
being passed to the inferior, meaning the signal disposition being
inherited by GDB's fork children.  However, we now call
restore_original_signals_state prior to forking, so the comment on
SIGTRAP is redundant.

The comments for SIGQUIT are similarly out of date, further, the
comment on SIGQUIT talks about problems with BSD4.3 and vfork,
however, we have not supported BSD4.3 for several years now.

Given the above, it seems that changing the disposition of SIGTRAP is
no longer needed, so I've deleted the signal() call for SIGTRAP.

Finally, the header comment on the function now called
gdb_init_signals was getting quite out of date, so I've updated it
to (hopefully) better reflect reality.

There should be no user visible change after this commit.

gdb/event-top.c

@@ -899,20 +899,21 @@ handle_sigsegv (int sig)
    handler.  */
 static struct serial_event *quit_serial_event;
 
-/* Initialization of signal handlers and tokens.  There is a function
-   handle_sig* for each of the signals GDB cares about.  Specifically:
-   SIGINT, SIGQUIT, SIGTSTP, SIGHUP, SIGWINCH.  These
-   functions are the actual signal handlers associated to the signals
-   via calls to signal().  The only job for these functions is to
-   enqueue the appropriate event/procedure with the event loop.  Such
-   procedures are the old signal handlers.  The event loop will take
-   care of invoking the queued procedures to perform the usual tasks
-   associated with the reception of the signal.  */
-/* NOTE: 1999-04-30 This is the asynchronous version of init_signals.
-   init_signals will become obsolete as we move to have to event loop
-   as the default for gdb.  */
+/* Initialization of signal handlers and tokens.  There are a number of
+   different strategies for handling different signals here.
+
+   For SIGINT, SIGTERM, SIGQUIT, SIGHUP, SIGTSTP, there is a function
+   handle_sig* for each of these signals.  These functions are the actual
+   signal handlers associated to the signals via calls to signal().  The
+   only job for these functions is to enqueue the appropriate
+   event/procedure with the event loop.  The event loop will take care of
+   invoking the queued procedures to perform the usual tasks associated
+   with the reception of the signal.
+
+   For SIGSEGV the handle_sig* function does all the work for handling this
+   signal.  */
 void
-async_init_signals (void)
+gdb_init_signals (void)
 {
   initialize_async_signal_handlers ();
 
@@ -926,21 +927,7 @@ async_init_signals (void)
     = create_async_signal_handler (async_sigterm_handler, NULL, "sigterm");
   signal (SIGTERM, handle_sigterm);
 
-  /* If SIGTRAP was set to SIG_IGN, then the SIG_IGN will get passed
-     to the inferior and breakpoints will be ignored.  */
-#ifdef SIGTRAP
-  signal (SIGTRAP, SIG_DFL);
-#endif
-
 #ifdef SIGQUIT
-  /* If we initialize SIGQUIT to SIG_IGN, then the SIG_IGN will get
-     passed to the inferior, which we don't want.  It would be
-     possible to do a "signal (SIGQUIT, SIG_DFL)" after we fork, but
-     on BSD4.3 systems using vfork, that can affect the
-     GDB process as well as the inferior (the signal handling tables
-     might be in memory, shared between the two).  Since we establish
-     a handler for SIGQUIT, when we call exec it will set the signal
-     to SIG_DFL for us.  */
   sigquit_token =
     create_async_signal_handler (async_do_nothing, NULL, "sigquit");
   signal (SIGQUIT, handle_sigquit);