docker: update to rust 1.42 and rustup 1.21.1

Update to the latest rustup release, which (since 1.20.0) installs
rustfmt and clippy by default:
https://blog.rust-lang.org/2019/10/15/Rustup-1.20.0.html

Also update the Rust toolchain version to 1.42.0 to match the version in
the CrOS build environment.

Additionally, add workarounds for sysroot of cargo clippy.

BUG=None
TEST=docker/build_crosvm_base.sh && docker/wrapped_smoke_test.sh
TEST=bin/clippy on workstation

Change-Id: I7ac4db92f4e5f277d77a77fa3c4ffa880f2ae116
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2150988
Tested-by: Keiichi Watanabe <keiichiw@chromium.org>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/bin/clippy b/bin/clippy
index 6631f26..03f85c8 100755
--- a/bin/clippy
+++ b/bin/clippy
@@ -72,5 +72,11 @@ SUPPRESS=(
 # Needed or else clippy won't re-run on code that has already compiled.
 cargo clean
 
+# Need to set pass --sysroot for cargo-clippy manually.
+# cf. https://github.com/rust-lang/rust-clippy/issues/3523
+RUST_SYSROOT=$(rustc --print sysroot)
+RUSTFLAGS="${RUSTFLAGS:-}"
+export RUSTFLAGS="$RUSTFLAGS --sysroot=$RUST_SYSROOT"
+
 cargo clippy --all-features --all-targets -- ${SUPPRESS[@]/#/-Aclippy::} "$@" \
       -D warnings