Dumping bitcode of core libraries

I have a cargo project where I can configure successfully that all crates should be dumped as bitcode (rustflags = ["--emit=llvm-bc"]). That way, I get a bunch of bitcode files in the deps folder of my cargo output.

I'm using no_std, however, I am also going to need alloc::fmt. Unfortunately that bitcode does not get dumped to deps. Is there a way to obtain it somehow? I know I could poke into some .rlib files that are stashed in the sysroot, but is there a less hacky way to do this?

(Ultimately, I want to link all the bitcode files using llvm-link.)