These tests take a good amount of time to run locally and they're also
causing a lot of dependencies to get pulled into rust-lang/rust, so
let's have a separate crate that we just test on our own CI
There's now a lock file upstream in rust-lang/rust so the one here isn't
actually used, and otherwise this crate is used as a dependency so the lock file
isn't respected anyway!
This configure script is similar to rust's in that it doesn't require anything
like autotools, it's just a meta-script to "generate" a makefile and perform
run-of-the-mill validation/discovery before the Makefile is run.
The main purpose of this rewrite is to support multi-target and targeted builds.
This will allow us to produce 32-bit snapshots for platforms as well as easily
providing `./configure --target $foo` for initialization.
cc #274
