ARM: Fix JNI MacroAssembler after VIXL update.

This patch fixes an issue found here:
https://android-review.googlesource.com/#/c/307532/

Also re-enables vixl MacroAssembler for arm.

Test: export ART_USE_READ_BARRIER=true; export ART_HEAP_POISONING=true; \
      m test-art-host
Test: export ART_USE_READ_BARRIER=true; export ART_HEAP_POISONING=true; \
      m test-art-target
Test: dump-oat-boot with ART_USE_READ_BARRIER=true

Change-Id: I03e3014fb250791db2d24a0ab1a76ca96384c332
2 files changed