Add mips64el to CI

.travis.yml

@@ -73,6 +73,7 @@ matrix:
     - env: TARGET=mips-unknown-linux-musl
     - env: TARGET=mipsel-unknown-linux-musl
     - env: TARGET=mips64-unknown-linux-gnuabi64
+    - env: TARGET=mips64el-unknown-linux-gnuabi64
     - env: TARGET=mips-unknown-linux-gnu
     - env: TARGET=s390x-unknown-linux-gnu
     - env: TARGET=asmjs-unknown-emscripten

ci/docker/mips64el-unknown-linux-gnuabi64/Dockerfile

+FROM ubuntu:17.10
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        gcc libc6-dev qemu-user ca-certificates \
+        gcc-mips64el-linux-gnuabi64 libc6-dev-mips64el-cross \
+        qemu-system-mips64el
+
+ENV CARGO_TARGET_MIPS64EL_UNKNOWN_LINUX_GNUABI64_LINKER=mips64el-linux-gnuabi64-gcc \
+    CARGO_TARGET_MIPS64EL_UNKNOWN_LINUX_GNUABI64_RUNNER="qemu-mips64el -L /usr/mips64el-linux-gnuabi64" \
+    CC_mips64el_unknown_linux_gnuabi64=mips64el-linux-gnuabi64-gcc \
+    PATH=$PATH:/rust/bin