Update sccache to its master branch

Ideally I'd like to soon enable sccache for rustbuild itself and some of the
stage0 tools, but for that to work we'll need some better Rust support than the
pretty old version we were previously using!

src/ci/docker/dist-various-1/Dockerfile

@@ -66,6 +66,14 @@ RUN env \
     bash musl.sh mipsel && \
     rm -rf /build/*
 
+# FIXME(mozilla/sccache#235) this shouldn't be necessary but is currently
+# necessary to disambiguate the mips compiler with the mipsel compiler. We want
+# to give these two wrapper scripts (currently identical ones) different hashes
+# to ensure that sccache understands that they're different compilers.
+RUN \
+  echo "# a" >> /usr/local/mips-linux-musl/bin/mips-openwrt-linux-musl-wrapper.sh && \
+  echo "# b" >> /usr/local/mipsel-linux-musl/bin/mipsel-openwrt-linux-musl-wrapper.sh
+
 ENV TARGETS=asmjs-unknown-emscripten
 ENV TARGETS=$TARGETS,wasm32-unknown-emscripten
 ENV TARGETS=$TARGETS,x86_64-rumprun-netbsd

src/ci/docker/run.sh

@@ -104,8 +104,6 @@ if [ "$SCCACHE_BUCKET" != "" ]; then
     args="$args --env SCCACHE_REGION"
     args="$args --env AWS_ACCESS_KEY_ID"
     args="$args --env AWS_SECRET_ACCESS_KEY"
-    args="$args --env SCCACHE_ERROR_LOG=/tmp/sccache/sccache.log"
-    args="$args --volume $objdir/tmp:/tmp/sccache"
 else
     mkdir -p $HOME/.cache/sccache
     args="$args --env SCCACHE_DIR=/sccache --volume $HOME/.cache/sccache:/sccache"

src/ci/docker/scripts/sccache.sh

@@ -13,6 +13,6 @@
 set -ex
 
 curl -fo /usr/local/bin/sccache \
-  https://s3-us-west-1.amazonaws.com/rust-lang-ci2/rust-ci-mirror/2017-05-12-sccache-x86_64-unknown-linux-musl
+  https://s3-us-west-1.amazonaws.com/rust-lang-ci2/rust-ci-mirror/2018-04-02-sccache-x86_64-unknown-linux-musl
 
 chmod +x /usr/local/bin/sccache