Abstract out fetching of break_address in debug mode

src/x87/assembler-x87.h

Index: src/x87/assembler-x87.h
diff --git a/src/x87/assembler-x87.h b/src/x87/assembler-x87.h
index 162416735b0be3150e9f6efa4a95de00d3f6fd1c..1edb2deb16337bf22a0a88fb31a3d6052fea02e0 100644
--- a/src/x87/assembler-x87.h
+++ b/src/x87/assembler-x87.h
@@ -502,6 +502,9 @@ class Assembler : public AssemblerBase {
   // of that call in the instruction stream.
   inline static Address target_address_from_return_address(Address pc);
 
+  // Return the code target address of the patch debug break slot
+  inline static Address break_address_from_return_address(Address pc);
+
   // This sets the branch destination (which is in the instruction on x86).
   // This is for calls and branches within generated code.
   inline static void deserialization_set_special_target_at(