Please update travis to use compiler-rt libs provided by llvm.org/apt/

[sylvestre]

Just like LLVM, could you please update the travis file .travis.yml to use the compiler_rt libraries provided in the llvm.org/apt/ package ?

$ wget http://llvm.org/apt/precise/pool/main/l/llvm-toolchain-snapshot/libclang-3.5-dev_3.5~svn213096-1~exp1_amd64.deb
$ dpkg -c libclang-3.5-dev_3.5~svn213096-1~exp1_amd64.deb |grep builtins
-rw-r--r-- root/root    223746 2014-07-16 02:20 ./usr/lib/llvm-3.5/lib/clang/3.5/lib/clang_linux/builtins-x86_64/libcompiler_rt.a

[huonw]

We no longer build rustc on travis, just run make tidy, so this no longer necessary.