Implement the 1.8 unsafe memory fences directly in HIR.

Rationale:
More efficient since it exposes full semantics to
all operations on the graph and allows for proper
code generation for all architectures.

bug=26264765

Change-Id: Ic435886cf0645927a101a8502f0623fa573989ff
diff --git a/compiler/optimizing/intrinsics.h b/compiler/optimizing/intrinsics.h
index 0cec5cc..3da8285 100644
--- a/compiler/optimizing/intrinsics.h
+++ b/compiler/optimizing/intrinsics.h
@@ -231,7 +231,10 @@
 UNREACHABLE_INTRINSIC(Arch, IntegerCompare)         \
 UNREACHABLE_INTRINSIC(Arch, LongCompare)            \
 UNREACHABLE_INTRINSIC(Arch, IntegerSignum)          \
-UNREACHABLE_INTRINSIC(Arch, LongSignum)
+UNREACHABLE_INTRINSIC(Arch, LongSignum)             \
+UNREACHABLE_INTRINSIC(Arch, UnsafeLoadFence)        \
+UNREACHABLE_INTRINSIC(Arch, UnsafeStoreFence)       \
+UNREACHABLE_INTRINSIC(Arch, UnsafeFullFence)
 
 }  // namespace art