Try using a newer gcc on travis

.travis.yml

@@ -20,14 +20,19 @@ script:
 notifications:
   email:
     on_success: never
+
+# Need gcc 4.7 for alignof/stdalign.h and we use multilib as we test both 32/64
 addons:
+  sources:
+    - ubuntu-toolchain-r-test
   apt:
     packages:
-      - gcc-multilib
+      - gcc-4.7-multilib
 env:
-  matrix:
+  - ARCH=x86_64 CC=gcc-4.7
-    - ARCH=x86_64
+  - ARCH=x86_64 CC=clang
-    - ARCH=i686
+  - ARCH=i686 CC=gcc-4.7
+  - ARCH=i686 CC=clang
 
 os:
   - linux