Revert "Revert "Fully support pairs in the register allocator.""

This reverts commit c399fdc442db82dfda66e6c25518872ab0f1d24f.

Change-Id: I19f8215c4b98f2f0827e04bf7806c3ca439794e5
diff --git a/compiler/optimizing/locations.cc b/compiler/optimizing/locations.cc
index 9f2f9ec..990d662 100644
--- a/compiler/optimizing/locations.cc
+++ b/compiler/optimizing/locations.cc
@@ -27,7 +27,7 @@
       temps_(instruction->GetBlock()->GetGraph()->GetArena(), 0),
       environment_(instruction->GetBlock()->GetGraph()->GetArena(),
                    instruction->EnvironmentSize()),
-      output_overlaps_(true),
+      output_overlaps_(Location::kOutputOverlap),
       call_kind_(call_kind),
       stack_mask_(nullptr),
       register_mask_(0),