[Bug c/60523] Warning flag for octal literals

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60523

--- Comment #6 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Octal literals are also used in macro definitions from system headers, so 
care would be needed that a warning doesn't apply to those.

Such a warning should of course not apply to 0 (and maybe more generally 
should not apply to any octal constant consisting of some number of 
leading 0s followed by at most one nonzero digit, as those have the same 
value whether interpreted as octal or as decimal).