zig rc: Add COFF object file creation for CMake cross-compilation use case

[squeek502]

This is a fully optional PR that addresses a use case that will only be temporarily supported, since all resinator code and the zig rc subcommand is likely to be removed when Windows resource compilation becomes a build system thing (see #22522 for context).

Is what's described below worth the temporary addition of an extra thousand+ lines of code?

Note: This only touches files within lib/compiler/resinator

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In #22522 I said:

RC="zig rc" will now work in combination with zig cc and CMake. Here's an example of cross-compiling a simple Windows GUI CMake project

$ RC="zig rc" CC="zig cc --target=x86_64-windows-gnu" cmake .. -DCMAKE_SYSTEM_NAME=Windows -G Ninja

However, I didn't realize at the time that this only works because of the -G Ninja part. When not using Ninja as the generator, CMake adds a workaround for 'very long lists of object files' where it takes all object files and runs them through ar to combine them into one archive:

https://github.com/Kitware/CMake/blob/4a11fd8dde745789f66d6500412d7f56607e9218/Modules/Platform/Windows-GNU.cmake#L141-L158

This is a problem for the Windows resource use-case, because ar doesn't know how to deal with .res files and so this object combining step fails with:

unknown file type: foo.rc.res

Only the linker knows what to do with .res files (since it has its own .res -> .obj ('cvtres') conversion mechanism). So, when using Ninja: this object file combining step is skipped, and the .res file gets passed to the linker and everyone is happy.

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When CMake thinks that it's using windres as the Windows resource compiler, it will pass -O coff to windres which causes it to output a COFF object file instead of a .res file, which means that the ar step can succeed because it's only working on actual object files.

This commit gives zig rc the ability to output COFF object files directly whenever /:output-format coff is provided as an argument. This effectively matches what happens when CMake uses windres for resource compilation, but requires the argument to be provided explicitly.

So, after this change, the following CMake cross-compilation use case will work, even when not using Ninja as the generator:

RC="zig rc /:output-format coff" CC="zig cc --target=x86_64-windows-gnu" cmake .. -DCMAKE_SYSTEM_NAME=Windows

[andrewrk]

Sure, let's do it. Thanks for the writeup.