Support multiple os

[samoht]

An example: currently, the package mirage-net-macosx depends on vmnet which is available on OSX only. That would be interesting to know that although the package is not available on linux, it is available on OSX.

The os variable can be overwritten easily by setting OPAMVAR_os properly:

OPAMVAR_os=darwin opam list

[rdicosmo]

OWS does not perform an analysis per-OS. There is no technical difficulty in adding it, but there is quite a bit of work to make the results readable: a "per-OS" version of the current page? a refinement of the current "per-compiler" columns with "per-OS" subcolumns? a per package page with all the matrix? And is the result worth the extra development effort?

[samoht]

I agree that we do not want to clutter the table with an other dimension. But maybe in case of conflicts, we should check if the root cause is the os mismatch issue and test with a different one.

But, on the current settings there is no way to "fix" mirage-net-macosx.

[abate]

I had completely missed this angle when I designed the ows page. I'm not sure how to add this. The notion of installability here is clearly universally quantified on all OSs ... But this information should definitely be present on the page, I'll think about it

[samoht]

It should be possible to tell opam to ignore os constraints (we can add an OPAMVAR_os=* or something similar).