Support executable target in multiple directories

[gildor478]

This feature request has been migrated from artifact #1668 on forge.ocamlcore.org. It was assigned to user102.

user22831 posted on 2016-08-31 21:16:53:

I would like to use OASIS, but I use multiple directories for my projects and this is currently unsupported unless I turn every directory into a library (which I don't want to do).

The other option is to manually modify the _tags file, but this is both ocamlbuild-specific and not something I'm interested in (for obvious reasons).