While the discussion about how to refactor test framework is not
finished (#1654), make this change: move `rm -rf build` in the
beginning of the test. For these reasons:
* it is useful to inspect the contents of the `build` directory
especially after the test failure
* if build crashes mid-test (e.g. process killed), next run should
not be affected by the `build` directory from the previous run
There's some missing flexibility in how foreign specifiers can be used with
scheme that is addressed here with minimal changes to how scheme specifiers
are read. This opens up uses for users that they otherwise would have had
to modify the compiler's support files to accomplish.