Travis: Use MacPorts instead of Homebrew

Homebrew tends to drop support for a macOS release the second that Apple
stops releasing security updates for it, and that makes HB difficult to
use with some of the Travis macOS images.  Furthermore, even on
supported macOS releases, HB sometimes tries to build GCC from source
even if a binary (bottle) is available.  Long story short, MacPorts just
generally has better backward compatibility.  MacPorts is also what I
personally use on the official libjpeg-turbo build machine.

.travis.yml

@@ -58,20 +58,17 @@ matrix:
         CMAKE_FLAGS="-DWITH_SIMD=0"
         CTEST_OUTPUT_ON_FAILURE=1
 
-addons:
-  homebrew:
-    brewfile: true
-    update: true
-
-cache:
-  directories:
-    - $HOME/Library/Caches/Homebrew
-
-before_cache:
-  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then brew cleanup; fi
-
 before_install:
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then
+      pushd $HOME/Downloads &&
+      curl -LO https://updates.cdn-apple.com/2019/cert/041-88384-20191011-3d8da658-dca4-4a5b-b67c-26e686876403/JavaForOSX.dmg &&
+      hdid JavaForOSX.dmg &&
+      sudo installer -pkg /Volumes/Java\ for\ macOS\ 2017-001/JavaForOSX.pkg -target / &&
+      hdiutil detach /Volumes/Java\ for\ macOS\ 2017-001 &&
+      curl -LO https://raw.githubusercontent.com/GiovanniBussi/macports-ci/master/macports-ci &&
+      . ./macports-ci install &&
+      sudo /opt/local/bin/port -N install gcc5 yasm md5sha1sum &&
+      popd &&
       git clone --depth=1 https://github.com/libjpeg-turbo/gas-preprocessor.git ~/src/gas-preprocessor &&
       ln -fs /Applications/Xcode.app /Applications/Xcode72.app;
     fi

Brewfile

@@ -1,4 +0,0 @@
-brew 'yasm'
-brew 'gcc@5'
-brew 'md5sha1sum'
-cask 'homebrew/cask-versions/java6'