bug#20509: compiler warns about cl-defmethod defined after use

[Glenn Morris]

Stefan Monnier wrote:

> While using cl-defmethod without a previous cl-defgeneric is supported,
> it's not recommended.

It's used without one in several places in Emacs:

emacs-lisp/eieio-custom.el:472:1:Warning: the following functions are not
    known to be defined: eieio-customize-object,
    eieio-custom-object-apply-reset, eieio-custom-widget-insert

emacs-lisp/eieio-speedbar.el:426:1:Warning: the following functions are not
    known to be defined: eieio-speedbar-make-tag-line,
    eieio-speedbar-object-children, eieio-speedbar-expand

cedet/ede/base.el:662:1:Warning: the following functions are not known to be
    defined: ede-buffer-header-file, ede-target-sourcecode,
    ede-buffer-documentation-files, ede-documentation,
    ede-html-documentation

cedet/ede/config.el:417:1:Warning: the following functions are not known to be
    defined: ede-config-get-configuration,
    ede-config-setup-configuration,
    ede-commit

cedet/ede/custom.el:216:1:Warning: the following functions are not known to be
    defined: ede-customize, ede-commit-project


etc etc.