message: Added gcc-5, 6, 8 and clang-5/6 to travis and allow failures
diff: @@ -5,18 +5,42 @@ sudo: false
  language: cpp
  matrix:
  + fast_finish: true # Don't wait for the builds that are allowed to fail
  include:
  + - env: C_COMPILER=gcc-5 CXX_COMPILER=g++-5 GENERATOR_NAME="Unix Makefiles"
  + addons: { apt: { packages: ["g++-5"], sources: ["ubuntu-toolchain-r-test"] } }
  +
  + - env: C_COMPILER=gcc-6 CXX_COMPILER=g++-6 GENERATOR_NAME="Unix Makefiles"
  + addons: { apt: { packages: ["g++-6"], sources: ["ubuntu-toolchain-r-test"] } }
  +
  - env: C_COMPILER=gcc-7 CXX_COMPILER=g++-7 GENERATOR_NAME="Unix Makefiles"
  addons: { apt: { packages: ["g++-7"], sources: ["ubuntu-toolchain-r-test"] } }
  + - env: C_COMPILER=gcc-8 CXX_COMPILER=g++-8 GENERATOR_NAME="Unix Makefiles"
  + addons: { apt: { packages: ["g++-8"], sources: ["ubuntu-toolchain-r-test"] } }
  +
  - env: C_COMPILER=clang-5.0 CXX_COMPILER=clang++-5.0 GENERATOR_NAME="Unix Makefiles"
  addons: { apt: { packages: ["g++-7", "clang-5.0"], sources: ["llvm-toolchain-trusty-5.0", "ubuntu-toolchain-r-test"] } }
  - # g++-7 is needed here - otherwise the build will fail because g++-4.8 libstdc++ is used.
  + # g++-7 is needed here - otherwise g++-4.8 libstdc++ is used.
  +
  + - env: C_COMPILER=clang-5.0 CXX_COMPILER=clang++-5.0 GENERATOR_NAME="Unix Makefiles"
  + addons: { apt: { packages: ["g++-8", "clang-5.0"], sources: ["llvm-toolchain-trusty-5.0", "ubuntu-toolchain-r-test"] } }
  +
  + - env: C_COMPILER=clang-6.0 CXX_COMPILER=clang++-6.0 GENERATOR_NAME="Unix Makefiles"
  + addons: { apt: { packages: ["g++-8", "clang-6.0"], sources: ["llvm-toolchain-trusty-6.0", "ubuntu-toolchain-r-test"] } }
  - os: osx
  env: C_COMPILER=clang CXX_COMPILER=clang++ GENERATOR_NAME="Xcode"
  osx_image: xcode9.2
  + allow_failures:
  + # These are additional combinations that we test but allow to fail, as they're either older compilers (g++-5) or
  + # uncommon combinations that would need some workarounds or updates to work.
  + - env: C_COMPILER=gcc-5 CXX_COMPILER=g++-5 GENERATOR_NAME="Unix Makefiles"
  + - env: C_COMPILER=gcc-8 CXX_COMPILER=g++-8 GENERATOR_NAME="Unix Makefiles"
  + - env: C_COMPILER=clang-5.0 CXX_COMPILER=clang++-5.0 GENERATOR_NAME="Unix Makefiles"
  + - env: C_COMPILER=clang-6.0 CXX_COMPILER=clang++-6.0 GENERATOR_NAME="Unix Makefiles"
  +
  install:
  - |
  if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
  