* lisp/emacs-lisp/pcase.el (pcase--split-pred): Handle `memq` pred.

* lisp/emacs-lisp/pcase.el (pcase--split-pred): Handle `memq` pred.

Improve handling of the `member` tests generated from (or 'a 'b 'c).
This will expand

    (pcase EXP ((and (or 1 2 3) (guard (FOO))) EXP1) (1 EXP2) (6 EXP3))

to

    (cond ((memql '(3 2 1) EXP)
           (cond ((FOO) EXP1) ((eql EXP 1) EXP2)))
          ((eql EXP 6) EXP3))

rather than to

    (cond ((memql '(3 2 1) EXP)
           (cond ((FOO) EXP1) ((eql EXP 1) EXP2) ((eql EXP 6) EXP3)))
          ((eql EXP 1) EXP2)
          ((eql EXP 6) EXP3))