travis: Deduplicate build instructions

All information, except for osx_image image, is identical between
the two jobs so we can avoid repeating it.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

.travis.yml

@@ -1,5 +1,7 @@
 sudo: required
-language: generic
+language: c
+compiler: clang
+os: osx
 
 branches:
   except:
@@ -18,31 +20,18 @@ addons:
 
 matrix:
   include:
-    - compiler: clang
-      language: c
-      os: osx
-      osx_image: xcode10.3
-      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
-    - compiler: clang
-      language: c
-      os: osx
-      osx_image: xcode11.3
+    - osx_image: xcode11.3
+    - osx_image: xcode10.3
+
 env:
+  global:
     - 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