Fix Mac fontconfig build

Fix Mac fontconfig build

The Mac fontconfig just #defines the cache directory, which works fine if fontconfig never has to look up any fonts (the case until now).  If it has to actually find fonts from the disk, the cache directory and config directory need to be properly defined as well as running fc-cache to populate the cache directory.

Populating the cache directory can take some time, but should only happen on a clean build.  To remove this extra time, we have to not build poppler on Mac, which can now be accomplished with GYP_DEFINES="skia_mac_poppler=0"

R=bungeman@google.com, epoger@google.com

Author: vandebo@chromium.org

Review URL: https://codereview.chromium.org/113203003

git-svn-id: http://skia.googlecode.com/svn/trunk@12994 2bbb7eff-a529-9590-31e7-b0007b416f81