[Bug c/85678] -fno-common should be default

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85678

--- Comment #10 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Jonathan Wakely from comment #9)
> C89 6.7p4 looks equivalent to C99 6.9p5, so I don't see why -std=c89 should
> imply -fcommon.

To reduce costs in upgrading to post-revision 278509 compilers.

-std=c89 implies old code. Old code relies on old behaviour. Providing
old behaviour by default means that compiler users don't have to
suddenly put "-fcommon" in all their old code Makefiles to get compilation.

I am not sure about intermediate cases like c99, but certainly
newer language standards (c11, ...) can adopt the new behaviour.