Warnings with newer Emacs versions

[dschrempf]

With Emacs 28, I get the following warnings:

path/to/pcre2el.el: Warning: Use keywords rather than deprecated positional arguments to `define-minor-mode' [2 times]
path/to/pcre2el.el: Warning: ‘merge’ is an obsolete alias (as of 27.1); use ‘cl-merge’ instead.