ppx compilation is broken when used in a library

e.g. my app has a dependency, and the dependency is doing a ppx on its own files.
It breaks because npm puts bs-platform in the node_modules directory of the app (b/c it's shared) but the ppx compilation step expects bs_tools_ppx.exe to be in the node_modules of the dependency.

The error:
```
sh: /[etc etc]/the-project/node_modules/the-library/node_modules/bs-platform/lib/bs_ppx_tools.exe: No such file or directory
```

The issue names no files, tests, or entry points. Reproduce a library dependency whose own files use PPX, then trace how the compilation step resolves bs_ppx_tools.exe across node_modules; done means the dependency's PPX compilation works with npm's shared installation layout.

Written by the indexing model from the issue text.