Revert ":construction_worker: using libc++ with Clang"

This reverts commit 41b2c69.

.travis.yml

@@ -51,7 +51,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['clang-5.0', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-5.0']
     after_success:
       - make clang_sanitize -j4
 
@@ -119,7 +119,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6']
-        packages: ['clang-3.6', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.6']
       coverity_scan:
         project:
           name: "nlohmann/json"
@@ -207,55 +207,55 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.5']
-        packages: ['clang-3.5', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.5']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-3.6
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6']
-        packages: ['clang-3.6', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.6']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-3.7
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.7']
-        packages: ['clang-3.7', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.7']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-3.8
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: ['clang-3.8', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.8']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-3.9
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: ['clang-3.9', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-3.9']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-4.0
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-4.0']
-        packages: ['clang-4.0', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-4.0']
 
   - os: linux
     compiler: clang
     env: COMPILER=clang++-5.0
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['clang-5.0', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-5.0']
 
   - os: linux
     compiler: clang
@@ -265,7 +265,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['clang-5.0', 'libc++-dev', 'libc++abi-dev']
+        packages: ['g++-6', 'clang-5.0']
 
 ################
 # build script #