Do not generate C resources for all possible toolchains

The resources data is generated for both GCC and MSVC toolchains, even though we know beforehand which toolchain we're going to compile it for. By dropping the data duplication we make the generated resources file faster to compile, especially when dealing with large embedded data, instead of relying on the C pre-processor to walk the whole file and discard the branch we're not using.

Fixes: #2492 (closed)