Merge pull request #1246 from aninf-wo/hethi/enable-travis-gcc-cache

enable Travis ccache to speed up CI builds

.travis.yml

@@ -7,7 +7,11 @@ install:
 # /usr/bin/gcc is 4.6 always, but gcc-X.Y is available.
 - if [ "$CXX" = "g++" ]; then export CXX="g++-4.9" CC="gcc-4.9"; fi
 # /usr/bin/clang is 3.4, lets override with modern one.
-- if [ "$CXX" = "clang++" ] && [ "$TRAVIS_OS_NAME" = "linux" ]; then export CXX="clang++-3.7" CC="clang-3.7"; fi
+- if [ "$CXX" = "clang++" ] && [ "$TRAVIS_OS_NAME" = "linux" ]; then export CXX="clang++-3.7" CC="clang-3.7"; ln -sf /usr/bin/ccache /$HOME/bin/$CXX; ln -sf /usr/bin/ccache /$HOME/bin/$CC; fi
+# ccache on OS X needs installation first
+- if [ "$TRAVIS_OS_NAME" = "osx" ]; then brew install ccache; export PATH="/usr/local/opt/ccache/libexec:$PATH"; fi
+# reset ccache statistics
+- ccache --zero-stats
 - echo ${PATH}
 - echo ${CXX}
 - ${CXX} --version
@@ -30,6 +34,10 @@ os:
   - linux
   - osx
 language: cpp
+cache: ccache
+before_cache:
+  # print statistics before uploading new cache
+  - ccache --show-stats
 compiler:
   - gcc
   - clang