Embeddig C code into Rust crate

[retep998]

@mattico

I believe that LTO works when linking Rust and C code

At the moment Rust emits fully compiled object files and libraries for the linker to link. External libraries are simply passed to the linker (or bundled into an rlib and passed that way) but never does Rust do LTO with external libraries. There is no LTO between Rust and C at the moment, but maybe in the future there could be.