Disable spurious -Wstringop-overflow for setjmp/longjmp (bug 26647)

[Joseph Myers]

On Fri, 30 Oct 2020, Florian Weimer via Libc-alpha wrote:

> Why can't we do this instead, given that's an internal function?
> 
> - extern int __sigsetjmp (struct __jmp_buf_tag __env[1],
> + extern int __sigsetjmp (struct __jmp_buf_tag __env *,
> 
> Or doesn't this remove the warning?

It's not really an internal function, the installed setjmp.h does:

# define sigsetjmp(env, savemask)       __sigsetjmp (env, savemask)

And the declarations in setjmp.h and pthread.h need to be consistent in 
use of array or pointer to avoid the warnings about inconsistency there.  
So declaring as a pointer would lose the checks that make sense for user 
code.

-- 
Joseph S. Myers
joseph@codesourcery.com