travis.yml: duplicate before_script for MacOSX

Rather than keep the hack in the global code lets "Think Different"
and have a special copy for MacOSX.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

.travis.yml

@@ -89,7 +89,6 @@ git:
 
 
 before_script:
-  - if [ "$TRAVIS_OS_NAME" == "osx" ] ; then export PATH="/usr/local/opt/ccache/libexec:$PATH" ; fi
   - if command -v ccache ; then ccache --zero-stats ; fi
   - mkdir -p ${BUILD_DIR} && cd ${BUILD_DIR}
   - ${SRC_DIR}/configure ${BASE_CONFIG} ${CONFIG} || { cat config.log && exit 1; }
@@ -240,6 +239,11 @@ matrix:
       os: osx
       osx_image: xcode10.3
       compiler: clang
+      before_script:
+        - export PATH="/usr/local/opt/ccache/libexec:$PATH"
+        - if command -v ccache ; then ccache --zero-stats ; fi
+        - mkdir -p ${BUILD_DIR} && cd ${BUILD_DIR}
+        - ${SRC_DIR}/configure ${BASE_CONFIG} ${CONFIG} || { cat config.log && exit 1; }
 
 
     # Python builds