message: don't use default libc++ installs
diff: @@ -22,15 +22,15 @@ addons_shortcuts:
  addons_clang39: &clang39
  apt:
  sources: [ 'ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-3.9' ]
  - packages: [ 'clang-3.9','libc++-dev','libc++abi-dev' ]
  + packages: [ 'clang-3.9' ]
  addons_clang40: &clang40
  apt:
  sources: [ 'ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-4.0']
  - packages: [ 'clang-4.0','libc++-dev','libc++abi-dev' ]
  + packages: [ 'clang-4.0' ]
  addons_clang50: &clang50
  apt:
  sources: [ 'ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
  - packages: [ 'clang-5.0', 'clang-tidy-5.0','libc++-dev','libc++abi-dev' ]
  + packages: [ 'clang-5.0', 'clang-tidy-5.0' ]
  addons_gcc5: &gcc5
  apt:
  sources: [ 'ubuntu-toolchain-r-test' ]
  