Silence prolog.el compilation.

Silence prolog.el compilation.

* lisp/progmodes/prolog.el: Don't require compile when compiling.
  -- not using any macros from it, it's just a cheap way to silence the
  compiler that actually produces one warning.
(compilation-shell-minor-mode, compilation-error-regexp-alist)
(compilation-forget-errors, compilation-fake-loc)
(compilation-parse-errors-function, compilation-error-list): Declare.
(prolog-inferior-mode): Require 'compile.