bug#23640: 25.1.50; Getting rid of compiler warnings

[Paul Eggert <eggert@cs.ucla.edu>]

Ken Brown wrote:
> Why not just unconditionally initialize the variables that gcc complains about?

That could make the code harder to understand. Someone who sees "int i = 0;" can 
reasonably infer that the 0 is needed, i.e., that a later part of the code needs 
the 0. Someone who sees "int i IF_LINT (= 0);" should be under no such illusion.

The tradition of hijacking the symbol 'lint' for GCC purposes has been used for 
many years in several GNU packages. As the problem you mention affects only 
optionally-generated warnings on non-GNU platforms, I suspect nobody has cared 
until now about the issue. Anyway, I changed Emacs master to use the symbol 
GCC_LINT instead; this should avoid the collision in names. Please give it a try.

The FreeBSD and Cygwin uses of 'lint' violate the C Standard. For example:

#define lint 1
#include <stdio.h>
_Noreturn int x;

This program violates a constraint so the C Standard requires a compile-time 
diagnostic, but from what you say on FreeBSD and Cygwin the compiler misbehaves 
and silently ignores the _Noreturn. I see that HBBroeker is independently making 
a similar point on the Cygwin mailing list 
<https://www.cygwin.com/ml/cygwin/2016-05/msg00405.html>.