message: drop unsupported travis configs
diff: @@ -39,7 +39,7 @@ matrix:
  # https://llvm.org/bugs/show_bug.cgi?id=22757
  # clang 3.6 C++17/14 Release libc++
  - - env: CLANG_VERSION=3.6 BUILD_TYPE=Release CPP=17 LIBCXX=On
  + - env: CLANG_VERSION=3.6 BUILD_TYPE=Release CPP=14 LIBCXX=On HEADERS=On
  os: linux
  addons: &clang36
  apt:
  @@ -50,12 +50,8 @@ matrix:
  sources:
  - ubuntu-toolchain-r-test
  - - env: CLANG_VERSION=3.6 BUILD_TYPE=Release CPP=14 LIBCXX=On HEADERS=On
  - os: linux
  - addons: *clang36
  -
  # clang 3.7 C++17/14 Release libc++
  - - env: CLANG_VERSION=3.7 BUILD_TYPE=Release CPP=17 LIBCXX=On
  + - env: CLANG_VERSION=3.7 BUILD_TYPE=Release CPP=14 LIBCXX=On HEADERS=On
  os: linux
  addons: &clang37
  apt:
  @@ -70,10 +66,6 @@ matrix:
  - sourceline: 'deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-3.7 main'
  key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
  - - env: CLANG_VERSION=3.7 BUILD_TYPE=Release CPP=14 LIBCXX=On HEADERS=On
  - os: linux
  - addons: *clang37
  -
  # clang 3.8 C++17/14 Release libc++
  - env: CLANG_VERSION=3.8 BUILD_TYPE=Release CPP=17 LIBCXX=On
  os: linux
  @@ -153,21 +145,6 @@ matrix:
  # os: linux
  # addons: *clang5
  - # gcc-4.9 C++17/C++14 Release
  - - env: GCC_VERSION=4.9 BUILD_TYPE=Release CPP=17
  - os: linux
  - addons: &gcc49
  - apt:
  - packages:
  - - g++-4.9
  - - valgrind
  - sources:
  - - ubuntu-toolchain-r-test
  -
  - - env: GCC_VERSION=4.9 BUILD_TYPE=Release CPP=14 HEADERS=On
  - os: linux
  - addons: *gcc49
  -
  # gcc-5 C++17/C++14 Release
  - env: GCC_VERSION=5 BUILD_TYPE=Release CPP=17
  os: linux
  