@alexcrichton I know what you means when you say "compiler-rt library is tiny and very easy to build", but the reality is that it doesn't build for our targets (I tried for thumb-unknown before I stubbed it out). The main issue was [this](https://github.com/llvm-mirror/compiler-rt/blob/ea9eb19ec0fea9d387bfe41bb187efd4a1a52fd5/lib/builtins/int_endianness.h), it isn't designed for an unknown OS. Either we let the linker complain that an LLVM instrinsic is undefined, or we force people to port/patch complier-rt for their own bare-metal platforms.