CI: Add arm build to travis (#4422)

* Add arm to travis build matrix
* Pin clang-3.5 build to ubuntu trusty
* Add ccache to build
This explicitly excludes macOS since the images don't come with ccache
installed and the install time is not justified by the time saved.

.travis.yml

@@ -6,6 +6,15 @@ os: linux
 
 matrix:
   include:
+    # gcc on arm64
+    - compiler: gcc
+      arch: arm64
+      addons:
+        apt:
+          packages:
+            - ccache
+      env: &Debug
+        - TRAVIS_CUBERITE_BUILD_TYPE=DEBUG CUBERITE_PATH=./Cuberite_debug
     # AppleClang
     # OSX workers are slower to start up.  Having these first in the build matrix makes travis faster overall.
     - os: osx
@@ -14,8 +23,7 @@ matrix:
         - TRAVIS_CUBERITE_BUILD_TYPE=RELEASE CUBERITE_PATH=./Cuberite
     - os: osx
       compiler: clang
-      env: &Debug
-        - TRAVIS_CUBERITE_BUILD_TYPE=DEBUG CUBERITE_PATH=./Cuberite_debug
+      env: *Debug
     # Default clang
     - compiler: clang
       env: *Release
@@ -23,10 +31,9 @@ matrix:
       env: *Debug
     # clang 3.5
     - compiler: clang
+      dist: trusty
       addons: &clang35
         apt:
-          sources:
-            - llvm-toolchain-precise-3.5
           packages:
             - clang++-3.5
             - clang-3.5
@@ -34,6 +41,7 @@ matrix:
         - CC=clang-3.5;CXX=clang++-3.5
       env: *Release
     - compiler: clang
+      dist: trusty
       addons: *clang35
       before_install:
         - CC=clang-3.5;CXX=clang++-3.5
@@ -56,7 +64,11 @@ matrix:
         - CC=gcc-4.8;CXX=g++-4.8
       env: *Debug
 
+before_script:
+  - export PATH=$(echo "$PATH" | sed -e 's/:\/usr\/lib\/ccache//')
 script: ./CIbuild.sh
+cache: ccache
+
 
 notifications:
   email:

CIbuild.sh

@@ -6,7 +6,14 @@ export CUBERITE_BUILD_SERIES_NAME="Travis $CC $TRAVIS_CUBERITE_BUILD_TYPE"
 export CUBERITE_BUILD_ID=$TRAVIS_JOB_NUMBER
 export CUBERITE_BUILD_DATETIME=`date`
 
-cmake . -DBUILD_TOOLS=1 -DSELF_TEST=1;
+# Use ccache if available
+if [ `which ccache` ]; then
+	export CCACHE_CPP2=true
+	CACHE_ARGS="-DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache"
+	echo "Using ccache installed at $(which ccache)"
+fi
+
+cmake . -DBUILD_TOOLS=1 -DSELF_TEST=1 ${CACHE_ARGS};
 
 echo "Building..."
 cmake --build . -- -j 2;