More C type errors by default for GCC 14

[Eli Zaretskii]

> From: Jonathan Wakely <jwakely.gcc@gmail.com>
> Date: Wed, 10 May 2023 13:30:10 +0100
> Cc: arsen@aarsen.me, dje.gcc@gmail.com, jakub@redhat.com, gcc@gcc.gnu.org
> 
> People are still using C to write new programs, and they are still
> making avoidable mistakes. The default for new code using new -std
> modes should be safer and less error prone.

I agree.  I just think that a warning strikes the right balance
between the two extremes.  And it is a balance, because once upon a
time, GCC didn't even warn about such code.