Fixes <https://issues.guix.gnu.org/50264>.
Reported by Lars-Dominik Braun <lars@6xq.net>.
This fixes a regression introduced in
fa81971cba whereby 'map/accumulate-builds'
would return REST (the tail of LST) without applying PROC on it. The
effect would be that 'lower-inputs' in (guix gexp) would dismiss those
elements, leading to derivations with correct builders but only a subset
of the inputs they should have had.
* guix/store.scm (map/accumulate-builds): Add #:cutoff parameter and
remove 'accumulation-cutoff' variable. Call PROC on the elements of
REST.
* tests/store.scm ("map/accumulate-builds cutoff"): New test.
