[dune] Fix Dune build in Windows.

In order for Dune to work in Windows we need to tweak some script
calls, they need a POSIX shell and the `(run ...)` / `(system ...)`
actions use `cmd.exe` on Windows.

Hopefully, we will rely less on `bash` when Dune can understand Coq
libraries. This affects shell scripts in `kernel/**.sh` for example.

It is interesting to see how faster the Coq Windows build is with Dune
+ Windows.

There are some problems with PATHs that prevent the test suite from
working, these will be fixed in a future PR.

1 files changed, 7 insertions, 2 deletions

diff --git a/tools/coq_dune.ml b/tools/coq_dune.ml
index 6681b79e38..68371edcb1 100644
--- a/tools/coq_dune.ml
+++ b/tools/coq_dune.ml
@@ -271,8 +271,13 @@ let exec_ifile f =
   match Array.length Sys.argv with
   | 1 -> f stdin
   | 2 ->
-    let ic = open_in Sys.argv.(1) in
-    (try f ic with _ -> close_in ic)
+    let in_file = Sys.argv.(1) in
+    begin try
+      let ic = open_in in_file in
+      (try f ic
+       with _ -> eprintf "Error: exec_ifile@\n%!"; close_in ic)
+      with _ -> eprintf "Error: cannot open input file %s@\n%!" in_file
+    end
   | _ -> eprintf "Error: wrong number of arguments@\n%!"; exit 1
 
 let _ =