[guix] Use CMake's PROJECT_NAME for source package

Summary: Currently this is hard-coded, but by adding the print-project-name target we can make it depend on cmake's project configuration.

Test Plan: @bot guix-linux

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D17179