More g++ testing on travis

.travis.yml

@@ -126,6 +126,26 @@ matrix:
       compiler: clang++
       env: UBSAN=1 TOOLSET=clang COMPILER=clang++ CXXSTD=11,14,1z UBSAN_OPTIONS=print_stacktrace=1
 
+    - os: linux
+      compiler: g++-4.7
+      env: TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=11
+      addons:
+        apt:
+          packages:
+            - g++-4.7
+          sources:
+            - ubuntu-toolchain-r-test
+
+    - os: linux
+      compiler: g++-4.8
+      env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=11
+      addons:
+        apt:
+          packages:
+            - g++-4.8
+          sources:
+            - ubuntu-toolchain-r-test
+
     - os: linux
       compiler: g++-4.9
       env: TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=11