Only install gcc-multilib when necessary

.travis.yml

@@ -34,10 +34,6 @@ matrix:
     - os: linux
       env: TARGET=aarch64-unknown-linux-gnu
       rust: nightly-2015-09-08
-addons:
-  apt:
-    packages:
-      - gcc-multilib
 notifications:
   email:
     on_success: never

ci/run-travis.sh

@@ -57,6 +57,10 @@ else
 
   # clang has better error messages and implements alignof more broadly
   export CC=clang
+
+  if [ "$TARGET" = "i686-unknown-linux-gnu" ]; then
+    sudo apt-get install gcc-multilib
+  fi
 fi
 
 mkdir .cargo