Add clang++-libc++, g++ 4.4, g++ 4.6 to Travis

.travis.yml

@@ -1,4 +1,4 @@
-# Copyright 2016, 2017 Peter Dimov
+# Copyright 2016, 2017, 2018 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
@@ -25,6 +25,26 @@ matrix:
     - os: linux
       env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11
 
+    - os: linux
+      compiler: g++-4.4
+      env: TOOLSET=gcc COMPILER=g++-4.4 CXXSTD=98,0x
+      addons:
+        apt:
+          packages:
+            - g++-4.4
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: g++-4.6
+      env: TOOLSET=gcc COMPILER=g++-4.6 CXXSTD=03,0x
+      addons:
+        apt:
+          packages:
+            - g++-4.6
+          sources:
+            - ubuntu-toolchain-r-test
+
     - os: linux
       env: TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11
       addons:
@@ -163,6 +183,14 @@ matrix:
             - ubuntu-toolchain-r-test
             - llvm-toolchain-trusty-5.0
 
+    - os: linux
+      compiler: clang++-libc++
+      env: TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=03,11,14,1z
+      addons:
+        apt:
+          packages:
+            - libc++-dev
+
     - os: osx
       env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
       osx_image: xcode9.1