Travis: use clang and gcc

.travis.yml

@@ -43,11 +43,18 @@ install:
 script:
     - if [ x${COVERITY_SCAN_BRANCH} != x1 ]; then make check; fi
 
-compiler: clang
 after_script:
     - if [ -n "$COVERAGE" ]; then coveralls --gcov-options; fi
 
+compiler:
+    - clang
+    - gcc
+
 matrix:
+    # Don't build on OS X with gcc
+    exclude:
+      - os: osx
+        compiler: gcc
     # Add a gcov build
     include:
         - compiler: gcc