This commit switches the default build system for Rust from the makefiles to
rustbuild. The rustbuild build system has been in development for almost a year
now and has become quite mature over time. This commit is an implementation of
the proposal on [internals] which slates deletion of the makefiles on
2016-01-02.
[internals]: https://internals.rust-lang.org/t/proposal-for-promoting-rustbuild-to-official-status/4368
This commit also updates various documentation in `README.md`,
`CONTRIBUTING.md`, `src/bootstrap/README.md`, and throughout the source code of
rustbuild itself.
Closes#37858
We hope to move to AppVeyor in the near future off of Buildbot + EC2. This adds
an `appveyor.yml` configuration file which is ready to run builds on the auto
branch. This is also accompanied with a few minor fixes to the build system and
such to accomodate AppVeyor.
The intention is that we're not switching over to AppVeyor entirely just yet,
but rather we'll watch the builds for a week or so. If everything checks out
then we'll start gating on AppVeyor instead of Buildbot!
