[Bug c/67093] incorrect -Wnonnull text for execl family of functions

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67093

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
And right before the quote you gave:
"An application that relies on such a feature or behavior cannot be assured to
be portable across conforming implementations."

So this might not be a full requirement of POSIX, it is not a portable to do
it.  So GCC warns about this case.