In some cases, `dune` needs to run cross-compiled executables

While working on https://github.com/toots/ocaml-sys-socket I noticed that, in order to have ctypes generate the proper C constants for the underlying socket structures when cross-compiling for windows, the binary that it generates needed to be run as a binary for the windows target.

I was able to work around it by using the system call instead of run and calling a wrapper that used wine or wine64. See: https://github.com/toots/ocaml-sys-socket/blob/master/src/sys-socket/types/dune#L10

I believe that this might become a fairly reasonable use case when writing low-level bindings. I know that ocaml-ffmpeg has the same issue.

Could it be possible to allow the user to run an executable as a target binary, possibly by also passing a wrapper for it, perhaps with default values such as wine for windows?

Start with the example in src/sys-socket/types/dune and compare its system call and wrapper usage with Dune's run behavior. Trace how cross-compilation targets and executable invocation are handled; done means the issue's target executable and optional wrapper use case is supported without the workaround.