AArch64 code alignment is 4 for OatWriter
AArch64 code alignment is 4 for OatWriter

OatWriter DCHECKs against ARM alignment, which is 8 and <= all
other architectures *except* AArch64, so that was fine before.

Change-Id: I55a11fe60cfbec889f2e8d8b0f489fe0930ebf6f

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst