msvc, mingw: do not use cygpath by default

[nojb]

The default value of use_cygpath is Try, contrary to what the help string https://github.com/ocaml/flexdll/blob/a60821e4c2cec5142ac2437e7605473cc4254ea9/cmdline.ml#L150 says.

Fixes #139

[nojb]

The mingw build fails with this change, needs to be investigated.

[dra27]

The mingw-w64 port under Cygwin definitely needs to do this to parse x86_64-w64-mingw32-gcc -print-search-dirs, but MSYS2 doesn't. cf. on Cygwin:

DRA@Thor ~
$ x86_64-w64-mingw32-gcc -print-search-dirs | fgrep libraries
libraries: =/usr/lib/gcc/x86_64-w64-mingw32/11/:/usr/lib/gcc/x86_64-w64-mingw32/11/../../../../x86_64-w64-mingw32/lib/x8./../x86_64-w64-mingw32/lib/../lib/:/usr/x86_64-w64-mingw32/sys-root/mingw/lib/x86_64-w64-mingw32/11/:/usr/x86_64-w64-mi2/11/../../../../x86_64-w64-mingw32/lib/:/usr/x86_64-w64-mingw32/sys-root/mingw/lib/

and on MSYS2:

DRA@Thor ~
$ gcc -print-search-dirs | fgrep libraries
libraries: =C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/;C:/msys64/mingw64/bin/../lib/gcc/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../x86_64-w64-mingw32/lib/x86_64-w64-mingw32/14.1.0/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../x86_64-w64-mingw32/lib/../lib/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../x86_64-w64-mingw32/14.1.0/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../lib/;D:/a/msys64/mingw64/lib/x86_64-w64-mingw32/14.1.0/;D:/a/msys64/mingw64/lib/../lib/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../x86_64-w64-mingw32/lib/;C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../;D:/a/msys64/mingw64/lib/

I haven't checked the history, but I think that the behaviour may have been different way back in the early days when the mingw port was accessed with gcc -mno-cygwin (and the system search dirs may have been hard-coded?), but I hadn't gone through the git history.

I think the best behaviour might be:

• Don't use cygpath at all for the MSVC port (as here already)
• For mingw, don't use cygpath as a default but do explicitly use it when parsing the search path for Cygwin only

I think all the pieces are in place for the second part, but for now a quick fix would just be to do the first (it's obviously unequivocally wrong to be calling cygpath for MSVC).

[nojb]

Thanks for the quick review (on a weekend) :)

for now a quick fix would just be to do the first (it's obviously unequivocally wrong to be calling cygpath for MSVC).

OK, I did this.

[dra27]

I'm still dithering over whether this is the right thing to do (versus updating the documentation!). What I'm wondering is whether there are any MSVC users out there (compiling in Cygwin - i.e. using Unix-like infrastructure) where they do end up passing Cygwin-style paths (e.g. for -I) and so where this has been quietly working?