Attached is the macro `cl-once-only*', which takes a symbol which is
bound to a list of form (such as those contained in a `&rest args' in
`defmacro') and binds that variable to a list of symbols where each
symbol is bound to the result of evaluating (in order) the corresponding
form.  The docstring provides an example which might illustrate what it
does better then I did here.

I don't expect this to be used too often but it could be somewhat handy
in macros with a `&rest args' which are supposed to be evaluated.

(My motivation for this is to use this macro in another patch which I
didn't want to make longer with out-of-scope additions.  If this is
considered not worth polluting the `cl-' namespace over I can just write
the forms by hand so it's fine either way.)