bug#50148: 27.2; `C-h v' for option doesn't say it's an option

[Drew Adams <drew.adams@oracle.com>]

1. emacs -Q

2. Evaluate this code:

(defvaralias 'new-foo 'old-foo)
(make-obsolete-variable 'old-foo 'new-foo "2021-08-21")

(defcustom new-foo 42 "..." :type 'integer :group 'convenience)

3. C-h v new-foo

Buffer *Help* shows only this:

  new-foo's value is 42

    This variable is an alias for 'old-foo'.

  Documentation:
  ...

It doesn't say that `new-foo' is a user option.  There's no link to
Customize for it.  That's the bug.
___

You may say that what should have been used is
`define-obsolete-variable-alias', instead of `defvaralias' and
`make-obsolete-variable':

  (define-obsolete-variable-alias 'old-foo 'new-foo "2021-08-21")
  (defcustom new-foo 42 "..." :type 'integer :group 'convenience)

And yes, if that's used then there's no such bug.

But my use case is to allow the result of byte compilation with older
Emacs versions to work also for newer versions.  (Perhaps there is
another way to ensure this - let me know.  In any case, this seems
like a bug to me - it seems like this should just work.)

In GNU Emacs 27.2 (build 1, x86_64-w64-mingw32)
 of 2021-03-26 built on CIRROCUMULUS
Repository revision: deef5efafb70f4b171265b896505b92b6eef24e6
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.19042
System Description: Microsoft Windows 10 Pro (v10.0.2009.19042.1083)