Use EXIT_SUCCESS and EXIT_FAILURE in all exit calls.

Use exit rather than returning from main, for consistency on VMS.
Call as_fatal instead of as_bad or as_warn followed by exit.

gas/config/obj-ieee.c

@@ -509,7 +509,7 @@ DEFUN_VOID (write_object_file)
   if (abfd == 0)
     {
       as_perror ("FATAL: Can't create %s", out_file_name);
-      exit (42);
+      exit (EXIT_FAILURE);
     }
   bfd_set_format (abfd, bfd_object);
   bfd_set_arch_mach (abfd, bfd_arch_h8300, 0);