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
On all platforms, reading from stdin where the actual stdin isn't present should
return 0 bytes as having been read rather than the entire buffer.
On Windows, handle the case where we're inheriting stdio handles but one of them
isn't present. Currently the behavior is to fail returning an I/O error but
instead this commit corrects it to detecting this situation and propagating the
non-set handle.
Closes#31167
