`--binaries` should automatically add .exe on Windows

[jhasse]

Using fish on Windows via MSYS2 the automatic suggestion to install the correct package only works when typing the full binary name, including .exe, see fish-shell/fish-shell#3428.

As it calling binaries on Windows works with and without the .exe extension, it would be great if pkgfile handled this automatically.

[falconindy]

Is there a preprocessor macro I can use to detect compilation on windows? I don't think this should be done for unixy installs.

[jhasse]

Yes, _WIN32 is only definied on Windows.