travis: disable link/SFML for mac

Currently the SFML brew does not compile in the travis mac environment,
so do not install SFML via `./installdeps` for brew if `$TRAVIS` is set,
and add `-DENABLE_LINK=OFF` to cmake options for the mac travis job.

Also try to cache the `/usr/local` directory, to make the brew installs
faster, if this even works.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

.travis.yml

@@ -71,12 +71,13 @@ matrix:
           script:
               - mkdir build
               - cd build
-              - cmake .. -DENABLE_SDL=ON -DENABLE_OPENAL=ON
+              - cmake .. -DENABLE_SDL=ON -DENABLE_OPENAL=ON -DENABLE_LINK=OFF
               - make -j2
               - ./visualboyadvance-m.app/Contents/MacOS/visualboyadvance-m --help
           cache:
               directories:
                   - "$HOME/.ccache"
+                  - /usr/local
 
 notifications:
     webhooks:

installdeps

@@ -1051,8 +1051,15 @@ brew_installdeps() {
 
     check brew -v update
 
+    brews="nasm cmake ccache ffmpeg gettext libpng pkg-config sdl2 wxmac ccache"
+
+    # sfml brew currently broken in the travis mac environment
+    if [ -z "$TRAVIS" ]; then
+        brews="$brews sfml"
+    fi
+
     set --
-    for f in nasm cmake ccache ffmpeg gettext libpng pkg-config sdl2 sfml wxmac ccache; do
+    for f in $brews; do
         if brew info "$f" | grep -Eq '^Not installed$'; then
             set -- "$@" "$f"
         fi