Undefined Symbols upon crate execution

First issue here, hope I'm following guidelines as closely as possible

Input C/C++ Header

// excerpt from __bindings.i
int c_function(...snip...); // this looks fine

// excerpt from bindings.rs
extern "C" {
    #[link_name = "\u{1}_c_function"]
    pub fn c_function(
        ...snip...
    ) -> ::std::os::raw::c_int;
}

Bindgen Invocation

println!("cargo:rustc-link-search=native={}/{}", cargo_manifest_dir, path_to_native_lib);

bindgen::Builder::default()
    .enable_cxx_namespaces()
    .raw_line("pub use self::root:*;") 
    .header("input.h")
    .generate()
    .expect("Unable to generate API bindings!");

In src/lib.rs:

// generalized...
include!(concat!(env!("OUT_DIR"), "bindings.rs"));

pub fn do_something_with_c_function () {
    ...snip...
    unsafe {
        ...snip...
    }
}

Actual Results

cargo build works, but cargo test with a minimal suite

use super::*;

#[test]
fn test_basic {
    do_something_with_c_function();
}

gives

= note: Undefined symbols for architecture x86_64:
            "_c_function", referenced from:
                my lib mylib::do_something_with_c_function::h653e2de7cade7ada in mylib-054bcda1fe20f5d1.49ritj0qqjv8vn1a.rcgu.o
          ld: symbol(s) not found for architecture x86_64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)

Expected Results

The function/symbols appear to actually be present in the {{snip}}.rcgu.o file, but yet can't be linked? The function is also extern "C"'d , so it shouldn't be mangled

Any hints/feedback would be greatly appreciated!

Start by running the minimal cargo test described in the issue, then inspect src/lib.rs, the generated bindings.rs, and the cargo rustc-link-search setting. Compare the generated extern symbol and the native library used during cargo build and cargo test; done means the minimal test links and runs successfully.