Merge #15

15: Build extra tools required for softdevteam/yk. r=ltratt a=vext01

We can't quite use the ykrustc snapshots for testing `yk` because cargo and rustfmt are absent. Let's build 'em.

Co-authored-by: Edd Barrett <vext01@gmail.com>

Author: bors[bot]

.buildbot.toml

@@ -4,5 +4,9 @@
 codegen-units = 0           # Use many compilation units.
 debug-assertions = true     # Turn on assertions in rustc.
 
+[build]
+extended = true
+tools = ["cargo", "rustfmt"]
+
 [llvm]
 assertions = true           # Turn on assertions in LLVM.