Prefer defcustom :local specifier

Prefer defcustom :local specifier

* lisp/dirtrack.el (dirtrack-list):
* lisp/emacs-lisp/lisp.el (defun-prompt-regexp):
* lisp/emulation/viper-init.el
(viper-related-files-and-buffers-ring):
* lisp/emulation/viper-util.el (viper-syntax-preference):
* lisp/erc/erc.el (erc-ignore-list):
* lisp/files.el (buffer-offer-save, backup-by-copying-when-mismatch):
* lisp/find-file.el (ff-pre-find-hook, ff-pre-load-hook)
(ff-post-load-hook, ff-not-found-hook, ff-file-created-hook)
(ff-case-fold-search, ff-always-in-other-window)
(ff-ignore-include, ff-quiet-mode, ff-other-file-alist)
(ff-search-directories):
* lisp/mh-e/mh-e.el (mh-scan-prog):
* lisp/newcomment.el (comment-column):
* lisp/obsolete/rlogin.el (rlogin-directory-tracking-mode):
* lisp/play/decipher.el (decipher-ignore-spaces):
* lisp/plstore.el (plstore-encrypt-to):
* lisp/proced.el (proced-format, proced-filter, proced-sort)
(proced-descend, proced-auto-update-flag, proced-tree-flag):
* lisp/progmodes/fortran.el (fortran-line-length):
* lisp/shell.el (shell-history-file-name):
* lisp/simple.el (goal-column, fill-prefix):
* lisp/vc/ediff-init.el (ediff-use-faces)
(ediff-highlight-all-diffs, ediff-autostore-merges):
* lisp/vc/ediff-merg.el (ediff-show-clashes-only)
(ediff-skip-merge-regions-that-differ-from-default): Prefer defcustom
:local specifier to using 'make-variable-buffer-local' directly.

(cherry picked from commit e20ce5fcc53593db5400596afee783d966ad2b2d)