DWARF and unwind support for AOT assembly output.

runtime/vm/assembler_arm.cc

Index: runtime/vm/assembler_arm.cc
diff --git a/runtime/vm/assembler_arm.cc b/runtime/vm/assembler_arm.cc
index 3618bcedf7154a7a7fe586c4765efda5f168bf47..07a77ab77b540ac29b87377ae87283b1c3bf917c 100644
--- a/runtime/vm/assembler_arm.cc
+++ b/runtime/vm/assembler_arm.cc
@@ -3190,7 +3190,9 @@ void Assembler::EnterFrame(RegList regs, intptr_t frame_size) {
     // Set FP to the saved previous FP.
     add(FP, SP, Operand(4 * NumRegsBelowFP(regs)));
   }
-  AddImmediate(SP, -frame_size);
+  if (frame_size != 0) {
+    AddImmediate(SP, -frame_size);
+  }
 }