X64 implementation of native ascii string compare.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 37f96a66ff67318185fc9cfe018fe8c2077e5ed3..1dc1c5d43de3b9e9f56611298a998b33c26c1eba 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -204,9 +204,12 @@ class MacroAssembler: public Assembler {
   // Is the value a positive tagged smi.
   Condition CheckPositiveSmi(Register src);
 
-  // Are both values are tagged smis.
+  // Are both values tagged smis.
   Condition CheckBothSmi(Register first, Register second);
 
+  // Are either value a tagged smi.
+  Condition CheckEitherSmi(Register first, Register second);
+
   // Is the value the minimum smi value (since we are using
   // two's complement numbers, negating the value is known to yield
   // a non-smi value).