Function create_informational_target_machine 

pub(crate) fn create_informational_target_machine(
    sess: &Session,
    for_cfg: bool,
) -> OwnedTargetMachine

If for_cfg is true then we are creating this machine for the purpose of populating [rustc_codegen_ssa::TargetConfig] based on what LLVM actually enables in this configuration. -Ctarget-feature should be ignored in that case since it is already processed separately.