bug#40671: [DOC] modify literal objects

[Eli Zaretskii]

> Cc: eggert@cs.ucla.edu, mattiase@acm.org, rms@gnu.org,
>  michael_heerdegen@web.de, ke.vigouroux@laposte.net, 40671@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sun, 26 Apr 2020 17:34:56 +0300
> 
> >    #include <string.h>
> >    int main (void) { return !strcpy ((char *)"a", "b"); }
> 
> If you go out of your way to avoid warnings, then indeed, the compiler 
> won't show them.
> 
> And typecasts are an easy way to turn compilation errors into runtime 
> errors, in general.

I think this shows the difference between CANNOT and SHOULD NOT, wrt
constants.