Don’t attempt to modify constant conses

Don’t attempt to modify constant conses

From a patch privately suggested by Mattias Engdegård on 2020-05-11
in a followup to Bug#40671.
* admin/charsets/cp51932.awk:
* admin/charsets/eucjp-ms.awk:
Generate code that does not modify constant conses.
* doc/misc/emacs-mime.texi (Encoding Customization):
* lisp/emacs-lisp/byte-opt.el (byte-compile-side-effect-free-ops):
* lisp/frameset.el (frameset-persistent-filter-alist):
* lisp/gnus/gnus-sum.el (gnus-article-mode-line-format-alist):
Use append instead of nconc.
* lisp/language/japanese.el (japanese-ucs-cp932-to-jis-map)
(jisx0213-to-unicode):
Use mapcar instead of mapc.
* lisp/language/lao-util.el (lao-transcription-consonant-alist)
(lao-transcription-vowel-alist):
* lisp/language/tibetan.el (tibetan-subjoined-transcription-alist):
Use copy-sequence.
* test/src/fns-tests.el (fns-tests-nreverse):
(fns-tests-sort, fns-tests-collate-sort)
(fns-tests-string-version-lessp, fns-tests-mapcan):
Use copy-sequence, vector, and list.