[PATCH] Clarify error message (PR middle-end/55859)

[Marek Polacek]

This patch clarifies the error message when using e.g. -Obar option,
except non-negative numbers we accept some other levels too.
Bootstrapped on x86_64-linux.  Ok for trunk?

2013-01-04  Marek Polacek  <pola...@redhat.com>

        PR middle-end/55859
        * opts.c (default_options_optimization): Clarify error message.

--- gcc/opts.c.mp       2013-01-04 02:48:33.116785922 +0100
+++ gcc/opts.c  2013-01-04 02:48:51.729870314 +0100
@@ -1,7 +1,6 @@
 /* Command line option handling.
    Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011,
-   2012
-
+   2012, 2013
    Free Software Foundation, Inc.
    Contributed by Neil Booth.
 
@@ -543,7 +542,8 @@ default_options_optimization (struct gcc
              const int optimize_val = integral_argument (opt->arg);
              if (optimize_val == -1)
                error_at (loc,
-                         "argument to %qs should be a non-negative integer",
+                         "argument to %qs should be a non-negative integer, "
+                         "'g', 's', or 'fast'",
                          "-O");
              else
                {
        Marek