* lisp/progmodes/vhdl-mode.el: Use lexical-binding

* lisp/progmodes/vhdl-mode.el: Use lexical-binding

Use #' to quote function names to get better compiler diagnostics.
Wrap some lines to avoid arguments "hidden" in positions that are easy
to misread.
Prefix unused arguments with a semi-colon to silence compiler warnings.
Fix a few comments that used ;;; even though they were not headings.

(vhdl-emacs-21): Delete variable.
Replace all uses with (not (featurep 'xemacs)) instead since `vhdl-mode`
has been incompatible with Emacs<21 for more than 10 years already.
(vhdl-prepare-search-1): Add Edebug declaration.
(vhdl-prepare-search-2): Add Edebug declaration and use
`with-syntax-table`.
(vhdl-visit-file): Add Edebug and indentation declaration.
Move the bulk of the code to a function for easier debugging.
(vhdl--visit-file): New function extracted from `vhdl-visit-file`.
Be careful not to modify syntax tables in unrelated buffers.
(vhdl-speedbar-refresh): Remove unused var `pos`.
(vhdl-backward-sexp): Remove unused var `last-forward`.
(vhdl-electric-tab, vhdl-minibuffer-tab, vhdl-line-expand):
Rename arg to avoid conflict with the `prefix-arg`
global variable.
(vhdl-align-region-1): Remove unused var `indent`.
(vhdl-character-to-event): Actually give a body to that poor function.
(vhdl-template-context): Remove unused vars `entity-exists` and `string`.
(vhdl-template-group): Remove unused var `start`.
(vhdl-template-argument-list): Remove unused var `start`.
(vhdl-port-paste-context-clause): Remove unused var `margin`.
(vhdl-port-paste-testbench): Remove unused var `source-buffer`.
(vhdl-hs-minor-mode): Declare function `hs-hide-all`.
(vhdl-get-hierarchy): Rename arguments `ent-alist`, `conf-alist`, and
`conf-key` and bind those dynamically scoped var via `let` instead
since arguments can't be dynamically scoped.
(vhdl-speedbar-insert-hierarchy, vhdl-compose-configuration-architecture):
Same thing with arguments `ent-alist` and `conf-alist`.
(vhdl-cache-version): Declare variable.
(speedbar-expand-line, speedbar-edit-line): Declare functions.
(vhdl-speedbar-update-current-unit): Declare before first use.
(vhdl-compose-new-component): Remove unused var `project`.
(lazy-lock-minimum-size): Declare variable.
(vhdl-submit-bug-report): Declare variable `reporter-prompt-for-summary-p`.