travis: add mingw build

Note that it can't actually be run via Wine on the new Travis infrastructure
yet. See: travis-ci/travis-ci#4171

.travis.yml

@@ -30,10 +30,23 @@ before_script:
   - test -n "$USE_SHELL" && eval '"$USE_SHELL" -c "./autogen.sh"' || ./autogen.sh
 
 script:
+  - if [ -n "$UNIVALUE_CONFIG" ]; then unset CC; unset CXX; fi
   - OUTDIR=$BASE_OUTDIR/$TRAVIS_PULL_REQUEST/$TRAVIS_JOB_NUMBER-$HOST
   - UNIVALUE_CONFIG_ALL="--prefix=$TRAVIS_BUILD_DIR/depends/$HOST --bindir=$OUTDIR/bin --libdir=$OUTDIR/lib"
   - ./configure --cache-file=config.cache $UNIVALUE_CONFIG_ALL $UNIVALUE_CONFIG || ( cat config.log && false)
   - make -s $MAKEJOBS $GOAL || ( echo "Build failure. Verbose build follows." && make $GOAL ; false )
   - export LD_LIBRARY_PATH=$TRAVIS_BUILD_DIR/depends/$HOST/lib
   - if [ "$RUN_TESTS" = "true" ]; then make check; fi
 
+matrix:
+  fast_finish: true
+  include:
+    - os: linux
+      compiler: gcc
+      env: UNIVALUE_CONFIG=--host=x86_64-w64-mingw32 RUN_TESTS=false
+      addons:
+        apt:
+          packages:
+            - g++-mingw-w64-x86-64
+            - gcc-mingw-w64-x86-64
+            - binutils-mingw-w64-x86-64