Add a stubbed-out implementation of FlowGraphCompiler for ia32 and arm.

runtime/vm/code_generator_x64.cc

Index: runtime/vm/code_generator_x64.cc
diff --git a/runtime/vm/code_generator_x64.cc b/runtime/vm/code_generator_x64.cc
index 66845887b75e4cd68469adb88b1a142a9fbd7188..83d1533b426ab0514de57db9c18e46a4b13204c9 100644
--- a/runtime/vm/code_generator_x64.cc
+++ b/runtime/vm/code_generator_x64.cc
@@ -218,8 +218,8 @@ void CodeGenerator::GeneratePreEntryCode() {
 // - No two descriptors of same kind have the same PC.
 // A function without unique ids is marked as non-optimizable (e.g., because of
 // finally blocks).
-static void VerifyPcDescriptors(const PcDescriptors& descriptors,
-                                bool check_ids) {
+void CodeGenerator::VerifyPcDescriptors(const PcDescriptors& descriptors,
+                                        bool check_ids) {
 #if defined(DEBUG)
   // TODO(srdjan): Implement a more efficient way to check, currently drop
   // the check for too large number of descriptors.