Auto merge of #3467 - RossSmyth:bumpSysroot, r=RalfJung

Bump rustc-build-sysroot to 0.4.6

Fixes #3313

Author: bors

cargo-miri/Cargo.lock

@@ -18,7 +18,7 @@ directories = "5"
 rustc_version = "0.4"
 serde_json = "1.0.40"
 cargo_metadata = "0.18.0"
-rustc-build-sysroot = "0.4.1"
+rustc-build-sysroot = "0.4.6"
 
 # Enable some feature flags that dev-dependencies need but dependencies
 # do not.  This makes `./miri install` after `./miri build` faster.