Check instead of relying on NOTREACHED

NOTREACHED was designed for traditional lint decades ago,
and _Noreturn now normally subsumes its function.
In the one case in Emacs where NORETURN might help and _Noreturn does
not, check for NOTREACHED instead of assuming it.
* lib-src/etags.c (main):
* src/xterm.c (x_connection_closed):
Remove NOTREACHED after a call to a _Noreturn function, as NOTREACHED
is no longer needed there.  Also, one of the NOTREACHEDs was
misplaced, which defeated traditional lint checking anyway.
* lib-src/pop.c (pop_getline): Redo so as to not need NOTREACHED.
* src/emacs.c (main): Use eassume (false) rather than NOTREACHED,
so that running with ENABLE_CHECKING catches any internal error
causing the toplevel Frecursive_edit to return.

lib-src/etags.c

@@ -1146,7 +1146,6 @@ main (int argc, char **argv)
 	  {
 	    error ("-o option may only be given once.");
 	    suggest_asking_for_help ();
-	    /* NOTREACHED */
 	  }
 	tagfile = optarg;
 	break;
@@ -1208,7 +1207,6 @@ main (int argc, char **argv)
       case 'w': no_warnings = true;				break;
       default:
 	suggest_asking_for_help ();
-	/* NOTREACHED */
       }
 
   /* No more options.  Store the rest of arguments. */
@@ -1227,13 +1225,11 @@ main (int argc, char **argv)
 
   if (help_asked)
     print_help (argbuffer);
-    /* NOTREACHED */
 
   if (nincluded_files == 0 && file_count == 0)
     {
       error ("no input files specified.");
       suggest_asking_for_help ();
-      /* NOTREACHED */
     }
 
   if (tagfile == NULL)

lib-src/pop.c

@@ -1275,7 +1275,7 @@ pop_getline (popserver server, char **line)
       server->buffer_index = 0;
     }
 
-  while (1)
+  while (true)
     {
       /* There's a "- 1" here to leave room for the null that we put
          at the end of the read data below.  We put the null there so
@@ -1288,7 +1288,7 @@ pop_getline (popserver server, char **line)
 	    {
 	      strcpy (pop_error, "Out of memory in pop_getline");
 	      pop_trash (server);
-	      return (-1);
+	      break;
 	    }
 	}
       ret = RECV (server->file, server->buffer + server->data,
@@ -1298,13 +1298,13 @@ pop_getline (popserver server, char **line)
 	  snprintf (pop_error, ERROR_MAX, "%s%s",
 		    GETLINE_ERROR, strerror (errno));
 	  pop_trash (server);
-	  return (-1);
+	  break;
 	}
       else if (ret == 0)
 	{
 	  strcpy (pop_error, "Unexpected EOF from server in pop_getline");
 	  pop_trash (server);
-	  return (-1);
+	  break;
 	}
       else
 	{
@@ -1332,7 +1332,7 @@ pop_getline (popserver server, char **line)
 	}
     }
 
-  /* NOTREACHED */
+  return -1;
 }
 
 /*

src/emacs.c

@@ -2084,8 +2084,7 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
 
   /* Enter editor command loop.  This never returns.  */
   Frecursive_edit ();
-  /* NOTREACHED */
-  return 0;
+  eassume (false);
 }
 
 /* Sort the args so we can find the most important ones

src/xterm.c

@@ -10044,7 +10044,6 @@ For details, see etc/PROBLEMS.\n",
     {
       fprintf (stderr, "%s\n", error_msg);
       Fkill_emacs (make_fixnum (70));
-      /* NOTREACHED */
     }
 
   totally_unblock_input ();