Duplicate lang item in crate 'compiler_builtins'. Do I need this crate (Is the current README obsolete)?

[jlb6740]

Hi ... I am not sure I need to use this crate. I am trying to build a rust based static library to link with a RTOS embedded application. Unfortunately I get all sorts of duplicate item errors (primarily compiler_builtins) when linking the rust static library (.a file) when compiling and linking with the image for the embedded device.

I've found that if I emit objects and link in the .o of my rust library before cargo xbuild based command links in compiler_intrinsics then I can almost get my embedded application to build, I just have one undefined reference of __rust_probstack. If I manually add this function by copying code from the compiler_builtin's source to my rust code for the static library I can get my embedded application to compile and at least start execution. I'd like to properly link in select compiler_builtin functions into my static library (.a file) without manually adding the code for __rust_probstack, but I am not having luck doing that. After reading the description, I was wondering if I could fine tune which functions I used from compiler_builtins by adding this crate. However when I add to my rust code:

#![feature(compiler_builtins_lib)]
extern crate compiler_builtins;

and add to my cargo.toml:

[dependencies.compiler_builtins]
git = "https://github.com/rust-lang-nursery/compiler-builtins"

I get a lot of duplicate lang item errors such as:
error: duplicate lang item in crate `compiler_builtins`: `i128_add`.
  |
  = note: first defined in crate `compiler_builtins`.

Obviously I do not know my way around the rust build system very well. I am having trouble understanding which blogs and instructions I am following are already obsolete for what I am looking to do. In particular it seems compiler_builtins are built and linked automatically as part of libcore so I am not sure how bringing in this crate could not cause these type of linking errors. Can someone help my understanding here? Also I am not sure how/when to consider dependencies on the stage0 vs stage1 vs stage2 rust compiler but is that important to understand and apply here? In what direction do I need to look for these compiler intrinsic linking woes.