.res files are compiled Windows resource files that get linked into executables/libraries. The linker knows what to do with them, but previously you had to trick Zig into thinking it was an object file (by renaming it to have the .obj extension, for example).

After this commit, the following works:

    zig build-exe main.zig resource.res

or, in build.zig:

    exe.addObjectFile("resource.res");

Closes #6488