Update TravisCI build to use Clang 3.7

.travis.yml

@@ -1,11 +1,16 @@
 addons:
   apt:
     packages:
+    - clang-3.7
     - lib32stdc++6
     - lib32z1-dev
     - libc6-dev-i386
+    - linux-libc-dev
     - gcc-multilib
     - g++-multilib
+    sources:
+    - llvm-toolchain-precise-3.7
+    - ubuntu-toolchain-r-test
 language: cpp
 sudo: false
 compiler:
@@ -17,5 +22,5 @@ before_script:
 script:
   - mkdir build && cd build
   - PATH="~/.local/bin:$PATH"
-  - python ../configure.py --enable-optimize --no-mysql
+  - CC=clang-3.7 CXX=clang-3.7 python ../configure.py --enable-optimize --no-mysql
   - ambuild