Function rustc_codegen_llvm::back::lto::run_fat

pub(crate) fn run_fat(
    cgcx: &CodegenContext<LlvmCodegenBackend>, 
    modules: Vec<FatLTOInput<LlvmCodegenBackend>>, 
    cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>
) -> Result<LtoModuleCodegen<LlvmCodegenBackend>, FatalError>

Performs fat LTO by merging all modules into a single one and returning it for further optimization.