build: set up build job for i686 targets

Author: tesuji

.travis.yml

@@ -56,6 +56,11 @@ matrix:
       env: BASE_TESTS=true
     - os: linux
       env: BASE_TESTS=true
+    # We cannot cross-compile on x86_64 toolchain for i686 target,
+    # but i686 toolchain could run on x86_64 system.
+    - os: linux
+      env: HOST_TOOLCHAIN=i686-unknown-linux-gnu
+      if: type = pull_request OR branch = master
     - os: windows
       env: CARGO_INCREMENTAL=0 BASE_TESTS=true OS_WINDOWS=true
 

setup-toolchain.sh

@@ -9,5 +9,10 @@ if [[ "$CI" == true ]] || ! command -v rustup-toolchain-install-master > /dev/nu
   cargo install -Z install-upgrade rustup-toolchain-install-master --bin rustup-toolchain-install-master
 fi
 
-rustup-toolchain-install-master -f -n master
+TOOLCHAIN=()
+if [[ -n "$HOST_TOOLCHAIN" ]]; then
+    TOOLCHAIN=('--host', "$HOST_TOOLCHAIN")
+fi
+
+rustup-toolchain-install-master -f -n master "${TOOLCHAIN[@]}"
 rustup override set master