Patch: update -fmessage-length docs

[Tom Tromey]

It turns out that -fmessage-length defaults to 0 even for g++.  This
patch updates the documentation to match.

Ok?

Tom

:ADDPATCH documentation:

Index: ChangeLog
from  Tom Tromey  <tromey@redhat.com>

	* doc/invoke.texi (Language Independent Options): Message length
	defaults to 0.

Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 123217)
+++ doc/invoke.texi	(working copy)
@@ -2394,10 +2394,8 @@
 @item -fmessage-length=@var{n}
 @opindex fmessage-length
 Try to format error messages so that they fit on lines of about @var{n}
-characters.  The default is 72 characters for @command{g++} and 0 for the rest of
-the front ends supported by GCC@.  If @var{n} is zero, then no
-line-wrapping will be done; each error message will appear on a single
-line.
+characters.  If @var{n} is zero (the default), then no line-wrapping
+will be done; each error message will appear on a single line.
 
 @opindex fdiagnostics-show-location
 @item -fdiagnostics-show-location=once