Add more -std variants to .travis.yml; disable constexpr tuple_for_each test on libc++11

.travis.yml

@@ -52,6 +52,12 @@ matrix:
     - os: linux
       env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=c++11
 
+    - os: linux
+      env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=c++14
+
+    - os: linux
+      env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=c++1z
+
     - os: linux
       env: TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=c++11
 
@@ -61,9 +67,18 @@ matrix:
     - os: linux
       env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=c++11
 
+    - os: linux
+      env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=c++14
+
+    - os: linux
+      env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=c++1z
+
     - os: osx
       env: TOOLSET=clang COMPILER=clang++ CXXSTD=c++11
 
+    - os: osx
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=c++14
+
 install:
   - cd ..
   - git clone -b $TRAVIS_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root

test/tuple_for_each_cx.cpp

@@ -9,7 +9,9 @@
 #include <boost/tuple_for_each.hpp>
 #include <boost/config.hpp>
 
-#if defined( BOOST_NO_CXX11_CONSTEXPR )
+// Technically std::tuple isn't constexpr enabled in C++11, but it works with libstdc++
+
+#if defined( BOOST_NO_CXX11_CONSTEXPR ) || ( defined( _LIBCPP_VERSION ) && __cplusplus < 201400L )
 
 int main() {}