[depends] Force PIC/PIE in native protobuf

Summary: The cmake build for protobuf is expected to set it automatically if the shared builds are not built, but it appears to not always be the case depending on the host (e.g. guix).

Test Plan: Run the linux gitian builds.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13542