rustbuild: Add support for crate tests + doctests

This commit adds support to rustbuild to run crate unit tests (those defined by
`#[test]`) as well as documentation tests. All tests are powered by `cargo test`
under the hood.

Each step requires the `libtest` library is built for that corresponding stage.
Ideally the `test` crate would be a dev-dependency, but for now it's just easier
to ensure that we sequence everything in the right order.

Currently no filtering is implemented, so there's not actually a method of
testing *only* libstd or *only* libcore, but rather entire swaths of crates are
tested all at once.

A few points of note here are:

* The `coretest` and `collectionstest` crates are just listed as `[[test]]`
  entires for `cargo test` to naturally pick up. This mean that `cargo test -p
  core` actually runs all the tests for libcore.
* Libraries that aren't tested all mention `test = false` in their `Cargo.toml`
* Crates aren't currently allowed to have dev-dependencies due to
  rust-lang/cargo#860, but we can likely alleviate this restriction once
  workspaces are implemented.

cc #31590

1 files changed, 0 insertions, 1 deletions

diff --git a/src/liballoc/Cargo.toml b/src/liballoc/Cargo.toml
index 5da0f1a10b9..0889ca9fc84 100644
--- a/src/liballoc/Cargo.toml
+++ b/src/liballoc/Cargo.toml
@@ -6,7 +6,6 @@ version = "0.0.0"
 [lib]
 name = "alloc"
 path = "lib.rs"
-test = false
 
 [dependencies]
 core = { path = "../libcore" }