X64 Crank: Implemented DoBranch and all *AndBranch comparisons.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index be837f0448716f105cdb557d60ef6e7444005696..65438702bfe66272bcc2c240f349391ff97ac678 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -707,6 +707,10 @@ class Assembler : public Malloced {
     arithmetic_op_32(0x1b, dst, src);
   }
 
+  void sbbq(Register dst, Register src) {
+    arithmetic_op(0x1b, dst, src);
+  }
+
   void cmpb(Register dst, Immediate src) {
     immediate_arithmetic_op_8(0x7, dst, src);
   }