[C/C++/Fortran] remove pedwarn0 and warning0 and fix PR 36901

[Joseph S. Myers]

On Mon, 4 Aug 2008, Manuel López-Ibáñez wrote:

> * locate_old_decl now always prints "note: previous definition of %q+D
> was here" instead of "error:" or "warning:".

This function should no longer need the G_ in the inform calls that it did 
when they were calls through a function pointer: inform is declared with a 
parameter called gmsgid so these strings should be automatically extracted 
for translation.

-- 
Joseph S. Myers
joseph@codesourcery.com