Allow static linking in the developer mode

Allow static linking in the developer mode

Previously, we have disallowed static linking (for good reasons).
However, there are legitimate reasons where static linking might be
useful, and one of the reasons is the OSS-Fuzz project that doesn't have
the libraries used for build, so static linking is the sane option here.

The static linking is still disallowed in the "production" builds, but
it's not possible to disable shared and enable static libraries when
used together with --enable-developer.