travis: add macOS Xcode 11.3 testing

Ideally we would test macOS 10.15 as the newest release, however, that
is not available in Travis yet. We can at least test newer XCode
versions though to get toolchain validation.
Reviewed-by: NFabiano Fidêncio <fidencio@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

.travis.yml

@@ -75,6 +75,21 @@ matrix:
         # macOS, but doing 'install' and 'dist' gives us some useful coverage
         - mkdir build && cd build
         - ../autogen.sh --prefix=$(pwd)/install-root && make -j3 && make -j3 install && make -j3 dist
+    - compiler: clang
+      language: c
+      os: osx
+      osx_image: xcode11.3
+      env:
+        - PATH="/usr/local/opt/gettext/bin:/usr/local/opt/ccache/libexec:/usr/local/opt/rpcgen/bin:$PATH"
+        - PKG_CONFIG_PATH="/usr/local/opt/libxml2/lib/pkgconfig"
+      before_script:
+        # Hack to blow away py2
+        - brew link --overwrite python
+      script:
+        # We can't run 'distcheck' or 'syntax-check' because they fail on
+        # macOS, but doing 'install' and 'dist' gives us some useful coverage
+        - mkdir build && cd build
+        - ../autogen.sh --prefix=$(pwd)/install-root && make -j3 && make -j3 install && make -j3 dist
 
 git:
   submodules: true