Try using clang 3.7

.travis.yml

@@ -52,6 +52,7 @@ matrix:
             - *default_packages
             - g++-multilib
             - libc6-dbg:i386
+            - llvm-toolchain-precise-3.7
     - env: CONF=debug   ARCH=x86_64 CXX11=ON CCACHE_CPP2=yes
       compiler: clang
     - env: CONF=debug   ARCH=x86    CXX11=OFF CCACHE_CPP2=yes
@@ -123,6 +124,7 @@ before_script:
 
 script:
   - >
+      if [ "$CXX" = "clang++" ]; then export CXX="clang++-3.7" CC="clang-3.7"; fi
       eval "ARCH_FLAGS=\${ARCH_FLAGS_${ARCH}}" ;
       (cd build && cmake
       -DRAPIDJSON_HAS_STDSTRING=ON