Reland parts of 'Use weak cells in map checks in polymorphic ICs'

src/x87/macro-assembler-x87.h

Index: src/x87/macro-assembler-x87.h
diff --git a/src/x87/macro-assembler-x87.h b/src/x87/macro-assembler-x87.h
index ad308a495829d3537fe8b67aa7d40fdc1a9681c9..32f58e9f68766748829a3644bfb1e011008b590b 100644
--- a/src/x87/macro-assembler-x87.h
+++ b/src/x87/macro-assembler-x87.h
@@ -277,6 +277,9 @@ class MacroAssembler: public Assembler {
     }
   }
 
+  void CmpWeakValue(Register value, Handle<WeakCell> cell, Register scratch);
+  void LoadWeakValue(Register value, Handle<WeakCell> cell, Label* miss);
+
   // ---------------------------------------------------------------------------
   // JavaScript invokes