build: move available-node variable to top

Currently node_use_openssl uses the available-node variable before it is
defined causing the conditions that use it before that point to
evaluate incorrectly. As an example running the target
test/addons/.docbuildstamp will currently be skipped:

$ make test/addons/.docbuildstamp
Skipping .docbuildstamp (no crypto)

With this commit the target will only be skipped if configured --without-ssl.

PR-URL: https://github.com/nodejs/node/pull/22356


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>