osx: initialize ccache in get_macpython_environment

This is a better place IMHO because it parallels where it's set up in docker.

osx_utils.sh

@@ -266,6 +266,15 @@ function set_py_vars {
 }
 
 function get_macpython_environment {
+    if [ $USE_CCACHE == 1 ]; then
+        brew install ccache
+        export PATH=/usr/local/opt/ccache/libexec:$PATH
+        export CCACHE_MAXSIZE=200M
+        export CCACHE_CPP2=1
+        
+        # Prove to the developer that ccache is activated
+        which clang
+    fi
     # Set up MacPython environment
     # Parameters:
     #     $version : [implementation-]major[.minor[.patch]]