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 that the time that this only works because of the `-G Ninja` part. When not using Ninja as the build tool, 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:
4a11fd8dde/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.
Note: When CMake thinks that its 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 when `/: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
