make build fails with `ls: src//Import.resi: No such file or directory`

[cdaringe]

Problem

$ make build
ls: src//Import.resi: No such file or directory

Research

I executed a git bisect process and traced this down to 5d3c440e6ca61602eb9cdfca900c30cacecdfbb6.

Repro:

git checkout 4f46be7 && make clean && make build && git checkout 5d3c440 && make clean && make build

makes sense. the associated commit was titled "require interface files", and Import has no interface file.