build: support LOCAL_*_32 and LOCAL_*_64

Support the following new variables based on whether the current multilib
target is 32 bit or 64 bit:
LOCAL_CFLAGS_32
LOCAL_CFLAGS_64
LOCAL_LDFLAGS_32
LOCAL_LDFLAGS_64
LOCAL_ASFLAGS_32
LOCAL_ASFLAGS_64
LOCAL_C_INCLUDES_32
LOCAL_C_INCLUDES_64

Change-Id: Ia868d56dff114be301bf8297eec768675f186927