With this change, gcc can now successfully compile a tiny program that
printfs an integer returned from a function, from a dynamically linked
library that it compiled as well.

Rustc however, is orders of magnitude more complex, and the next step is
to fix constructors which require access to `environ`, in ld.so

Rust's libstd for example uses environ when using the `envs` builder
method for spawning processes, and therefore relibc cannot simply assume
environ will always point to the internal relibc env var Vec.