Fix seeder in the gitian build

Summary: Compat.h was removed in D2728 but didn't clean it up from the build.

Test Plan: Run a gitian build an verify that it completes successfully.

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: schancel

Differential Revision: https://reviews.bitcoinabc.org/D2733