dune-configurator for MSVC

[jonahbeckford]

Expected Behavior

I have been maintaining the patch at https://github.com/diskuv/diskuv-opam-repository/blob/main/packages/dune-configurator/dune-configurator.2.9.3/files/custom.patch which lets MSVC work when dune-configurator is used.

If we were creating a test file on Windows, the -o flags should instead be one of the following flags:

-Fotest.obj
-Fetest.exe

Actual Behavior

          cl dkml-runtime-apps/duniverse/ocaml-sha/sha512_stubs.obj
sha512_stubs.c
    discover dkml-runtime-apps/duniverse/dkml-c-probe/src/c_abi.ml (exit 2)
(cd _build/default/dkml-runtime-apps/duniverse/dkml-c-probe/src && config/discover.exe)
compiling c program:
 | #include <stdio.h>
 | #include <discover_osinfo.h>
 |
 | const char *s0 = "BEGIN-0-" DKML_OS_NAME "-END";
run: cl -nologo -O2 -Gy- -MD    -I Z:\dow1\dkml\_opam\.opam-switch\build\dune.2.9.3+shim.1.0.1\_build\default\dkml-runtime-apps\duniverse\dkml-c-probe\src -I Z:/dow1/lib/ocaml -o C:\Users\beckf\AppData\Local\Temp\buildfd33e7.dune\ocaml-configurator287304\c-test-0\test.obj -c C:\Users\beckf\AppData\Local\Temp\buildfd33e7.dune\ocaml-configurator287304\c-test-0\test.c
-> process exited with code 0
-> stdout:
 | test.c
-> stderr:
 | cl : Command line warning D9035 : option 'o' has been deprecated and will be removed in a future release
Fatal error: exception Sys_error("C:\\Users\\beckf\\AppData\\Local\\Temp\\buildfd33e7.dune\\ocaml-configurator287304\\c-test-0\\test.obj: No such file or directory")

Reproduction

This needs the MSVC compiler and a Cygwin/MSYS2 environment:

git clone https://github.com/diskuv/dkml-runtime-apps.git
cd dkml-runtime-apps
git switch 4c2fe53328ef3bb9b68c931b2c174847fb44b04d
opam install .

Additional information

I looked at the latest Dune code in the main branch ... it still uses the -o option for the name of the object and executable. (This is one of the reasons I haven't yet upgraded the Windows Diskuv OCaml distribution past Dune 2.9 yet.)

I'll bump up the priority of #6535 so this bug report can be verified.