MemoryHeapBase: ifdef for gingerbread compatibility

Allow to "revert" by a board config flag the offset member addon
see commit f24c4cd0 (aosp change id Ie618fb5c0718e)

This change is required to use overlay based proprietary camera libs
coming from gingerbread and froyo builds.

This change also requires a global cflag named BINDER_COMPAT
because a lot of modules use the MemoryHeap includes

Add this in your BoardConfig.mk :
COMMON_GLOBAL_CFLAGS += -DBINDER_COMPAT

Change-Id: Ib0370fbf4c4770f8141607a8fc393639ffbdc8e2