C99

I'd like to draw attention to this patch:

    http://sourceware.org/ml/gdb-patches/2013-06/msg00808.html

This points out that gdb has been unconditionally using a GCC extension,
apparently since at least 2010; the patch introducing the varargs define
in tracepoint.c was 7c56ce7 (2010-04-09).

The patch proposes replacing this with the corresponding C99 construct.

So, I'd like to propose we allow the use of C99 in gdb.  In particular I
think we ought to require a C99 preprocessor -- enabling this particular
patch to go in and also allowing the use of "//" comments.

Tom