Fixed and refactored 64b host build

Add a global variable ART_HOST_ARCH in build/Android.common.mk that
will be set to x86 or x86_64 depending on BUILD_HOST_64bit. This is
then used as the instruction set for dex2oat.

Change-Id: Icec8ef9139f780314a3ff325a729750e65d6d8da
3 files changed