The tests currently fail when run on riscv-linux (affecting the guix package)
because Guile 3 is used as the bootstrap guile. Correcting the package
version seems hard, so I'm just tweaking the tests to use the right effective
version for riscv64-linux.
* tests/gexp.scm (bootstrap-guile-effective-version): New procedure.
("gexp->derivation & with-extensions", "lower-gexp", "lower-gexp,
raw-derivation-file"): Use bootstrap-guile-effective-version.
Change-Id: I3995e1f6b58ada1baf38a8ec55b0173059dd0079