mail/mew: Prevent .el files from being native compiled

Mew doesn't work correctly if Emacs supports native compilation and
.el files are compiled to .eln ones. So prevent .el files from being
native compiled by adding following lines at the end of them.

;; Local Variables:
;; no-native-compile: t
;; End:

PR: 258171
Approved by: maintainer timeout (> 28days), meta (mentor)