message: Try using lld in CI
  lld is better in some ways that GNU ld, so maybe this will fix our
  issues with crashes in CI.
diff: @@ -8,7 +8,8 @@ LABEL maintainer="Martin Thomson <mt@lowentropy.net>"
  RUN apt-get update && apt-get install -y --no-install-recommends \
  ca-certificates coreutils curl git make mercurial ssh \
  - build-essential clang llvm libclang-dev gyp ninja-build pkg-config zlib1g-dev sudo \
  + build-essential clang llvm libclang-dev lld \
  + gyp ninja-build pkg-config zlib1g-dev sudo \
  && apt-get autoremove -y && apt-get clean -y \
  && rm -rf /var/lib/apt/lists/*
  @@ -38,7 +39,8 @@ USER $USER
  ENV NSS_DIR=$HOME/nss \
  NSPR_DIR=$HOME/nspr \
  - LD_LIBRARY_PATH=$HOME/dist/Debug/lib
  + LD_LIBRARY_PATH=$HOME/dist/Debug/lib \
  + RUSTFLAGS="-C link-arg=-fuse-ld=lld"
  RUN set -eux; \
  hg clone -u c7a1c91cd9be https://hg.mozilla.org/projects/nss "$NSS_DIR"; \
  