Automatic translation of object files in install stanzas for MSVC

[dra27]

Related: #690, #962, #1189

IIRC Dune automatically adds .exe to filenames when installing executables for Windows contexts. In addition to the support for variables in the referenced PRs, I'm wondering if it would be better for Dune to perform automatic conversion of items ending .o to .obj and .a to .lib for contexts using the Microsoft C compiler.

There might want to be some kind of syntax or semantics which prevents this kind of translation for very special cases (for example FlexDLL) where you might manipulate both .o and .obj files in the same place. However, for 99% of cases, writing .o in a dune is not portable.

[ghost]

I wondered about this as well. It would definitely be easier for Linux programmers. However, I wonder how intuitive it would be for others, such as OSX programmers as I believe the extensions are already different.

[dra27]

I didn’t know that - what’s the extension on macOS?

[ghost]

I think there are several possible choices, but I'm not sure. Maybe @rgrinberg or @avsm know more.

What about windows users BTW? Will it be clear to them that they should write .o?

[rgrinberg]

Extensions on OSX seems Unix like to me:

ext_exe: 
ext_obj: .o
ext_asm: .s
ext_lib: .a
ext_dll: .so

I'm wondering if we should simply start with warning the user when they use these unportable extensions. I'm not sure if the automatic translation in rules is very intuitive.

[avsm]

Only difference on osx is that there are special frameworks and .dylib extensions, but those are only as a result of explicit invocations. The rest is quite similar to Linux