Fix DBC build.

runtime/vm/intermediate_language_dbc.cc

Index: runtime/vm/intermediate_language_dbc.cc
diff --git a/runtime/vm/intermediate_language_dbc.cc b/runtime/vm/intermediate_language_dbc.cc
index e239229032ea9923933f9abd9ffe339f233a1028..859f7d432f3faa8106d55636a27ca97ab0e79fbd 100644
--- a/runtime/vm/intermediate_language_dbc.cc
+++ b/runtime/vm/intermediate_language_dbc.cc
@@ -92,6 +92,7 @@ DECLARE_FLAG(int, optimization_counter_threshold);
   M(Float64x2ZeroArg)                                                          \
   M(Float64x2OneArg)                                                           \
   M(CheckedSmiOp)                                                              \
+  M(CheckedSmiComparison)                                                      \
 
 // Location summaries actually are not used by the unoptimizing DBC compiler
 // because we don't allocate any registers.
@@ -179,6 +180,10 @@ FOR_EACH_UNREACHABLE_INSTRUCTION(DEFINE_UNREACHABLE)
 #undef DEFINE_UNREACHABLE
 
 
+// Only used in AOT compilation.
+DEFINE_UNIMPLEMENTED_EMIT_BRANCH_CODE(CheckedSmiComparison)
+
+
 EMIT_NATIVE_CODE(InstanceOf, 2, Location::SameAsFirstInput(),
                  LocationSummary::kCall) {
   SubtypeTestCache& test_cache = SubtypeTestCache::Handle();