Added support for unsigned comparisons

Rationale: even though not directly supported in input graph,
           having the ability to express unsigned comparisons
           in HIR is useful for all sorts of optimizations.

Change-Id: I4543c96a8c1895c3d33aaf85685afbf80fe27d72
diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 078d8e5..17c851c 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -615,6 +615,8 @@
   VisitCondition(condition);
 }
 
+// TODO: unsigned comparisons too?
+
 void InstructionSimplifierVisitor::VisitCondition(HCondition* condition) {
   // Try to fold an HCompare into this HCondition.