Improve sharpening for read barrier image HLoadClass

Handle MarkInBoot image for LoadKind::kReferrersClass. This reduces
read barriers for the boot image if the referring class is in
the boot image.

Only really helps CC case, TODO avoid doing the work for non CC?

ARM64 CC baker boot.oat: 48006064 -> 47916736

Bug: 29516974

Test: test-art-host CC baker

Change-Id: Ibfa0cf0a3b888ad0e53c2d95a38e330b79e7443c
1 file changed