Use "[warning enabled by default]" for default warnings

[Richard Sandiford <rdsandiford at googlemail dot com>]

We print "[-Wfoo]" after a warning that was enabled by the -Wfoo option,
which is pretty clear.  But for warnings that have no -W option we just
print "[enabled by default]", which leads to the question of _what_ is
enabled by default.  As shown by:

   http://gcc.gnu.org/ml/gcc/2014-01/msg00234.html

it invites the wrong interpretation for things like:

   warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]

IMO the natural assumption is that gnu++11 is enabled by default, which is
how Lars also read it.

There seemed to be support for using "warning enabled by default" instead,
so this patch does that.  Tested on x86_64-linux-gnu.  OK to install?

I'll post an Ada patch separately.

Thanks,
Richard


gcc/
	* opts.c (option_name): Use "warning enabled by default" rather than
	just "enabled by default".

gcc/testsuite/
	* gcc.dg/gomp/simd-clones-5.c: Update comment for new warning message.

Index: gcc/opts.c
===================================================================
--- gcc/opts.c	2014-02-09 12:07:06.237317560 +0000
+++ gcc/opts.c	2014-02-09 12:07:06.371318597 +0000
@@ -2222,7 +2222,7 @@ option_name (diagnostic_context *context
       if (context->warning_as_error_requested)
 	return xstrdup (cl_options[OPT_Werror].opt_text);
       else
-	return xstrdup (_("enabled by default"));
+	return xstrdup (_("warning enabled by default"));
     }
   else
     return NULL;
Index: gcc/testsuite/gcc.dg/gomp/simd-clones-5.c
===================================================================
--- gcc/testsuite/gcc.dg/gomp/simd-clones-5.c	2014-02-09 12:07:06.237317560 +0000
+++ gcc/testsuite/gcc.dg/gomp/simd-clones-5.c	2014-02-09 12:07:06.371318597 +0000
@@ -3,7 +3,7 @@
 
 /* ?? The -w above is to inhibit the following warning for now:
    a.c:2:6: warning: AVX vector argument without AVX enabled changes
-   the ABI [enabled by default].  */
+   the ABI [warning enabled by default].  */
 
 #pragma omp declare simd notinbranch simdlen(4)
 void foo (int *a)