how do i exec while passing OLDPWD?

related [but for bash]:
http://unix.stackexchange.com/questions/242909/why-does-bash-clear-oldpwd-when-a-child-script-is-started
 QUOTE: It seems reasonable to inherit OLDPWD if it names a directory, in
the same way that the shell inherits PWD if it names the current directory,
so we'll try that for the next bash version.