Create and enable auto-updater for MacOS using `Sparkle=1.23`. We need
to sign our app using an `Apple Developer Key` for it to work properly,
since we are not going to sign updates with the Sparkle key.
Add all auto-updater files to `gettext`'s pot.
Use `str_split` to always get related stable version. We do not want
to check for nightly builds.
For Windows, we create the flag `-DHTTPS` to select between using an
HTTPS or HTTP URL for the auto-updater checks. We use this to keep
support for Windows XP (HTTP only) while all others should be HTTPS.
Also, use `::FreeLibrary` to allow us to remove the temporary file
that stores the `WinSparkle.dll`. Previously, we could not get it to
work with `wine`.
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