Multiple GCC and Clang versions on TravisCI

.travis.yml

sudo: false
language: generic

cache:
  apt: true

matrix:
  include:
    - env: CXX=g++-5 CC=gcc-5
      addons:
        apt:
          packages:
            - g++-5
          sources: &sources
            - ubuntu-toolchain-r-test
            - llvm-toolchain-precise
            - llvm-toolchain-precise-3.7
            - llvm-toolchain-precise-3.6
    - env: CXX=g++-4.9 CC=gcc-4.9
      addons:
        apt:
          packages:
            - g++-4.9
          sources: *sources
    - env: CXX=clang++-3.8 CC=clang-3.8
      addons:
        apt:
          packages:
            - clang-3.8
          sources: *sources
    - env: CXX=clang++-3.7 CC=clang-3.7
      addons:
        apt:
          packages:
            - clang-3.7
          sources: *sources
    - env: CXX=clang++-3.6 CC=clang-3.6
      addons:
        apt:
          packages:
            - clang-3.6
          sources: *sources