Build external libs statically in the DISABLE_DYNLOADING case

Fixes build for iOS.

In theory, it is a bit unclear whether DISABLE_DYNLOADING means to 1)
not build any dynamic libraries at all, not even of bundled 3rd-party
libraries, or 2) not build any own dynamic libraries, including
dynamically loaded UNO components, while still building 3rd-party
libraries as dynamic. But in practice, a use case for the latter is
nonexistent, nobody uses --disable-dynamic-loading in their
autogen.input, and DISABLE_DYNLOADING is turned on automatically for
iOS and Android.

What we want for iOS, for an LO-based app, is to not build any dynamic
libraries at all, but produce a single executable. Correspondingly for
Android, at least currently, we want to produce a single dynamic
library.

Change-Id: I7af4c3e53b13439612bb57bbb0fc8b118bda96bd