Sync patch r2668 from BTT.
Fix GCC build rules for ASL sources that contain PCDs.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/branches/UDK2014@15569 6f19259b-4bc3-4df7-8a09-765794883524