(elisp--local-variables): Fix recent regression

(elisp--local-variables): Fix recent regression

While at it, make it work when completing code within `eval-when-compile`
and friends, where it failed in sometimes spectacular ways.

* lisp/progmodes/elisp-mode.el (elisp--local-macroenv): New var.
(elisp--local-variables): Use it.  Also, advice `macroexpand-1` since
`macroexpand-all` doesn't use `macroexpand` any more.
(prin1-char): Remove redundant "" arg.
(elisp--eval-defun-1): Align the `eval` call to what's used in
`custom-initialize-set`.