Commit d38f9934 ("[API CHANGE]
Asserts to never clear already cleared guard") changes the API
in a way, which can silently break compiling code for no reason.

As discussed on the mailing list, this uses LIBO_INTERNAL_ONLY to
restores the old behaviour for external API users.

Change-Id: I43c9b955c1c8f5402588fcea2bfc38ab6fa9f263
Reviewed-on: https://gerrit.libreoffice.org/70528Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Jenkins