Added thin-lock fast path for monitor-enter/exit on x86.

Change-Id: Iba187ae1acde6e341ae510d4b47f59e6984fc354
diff --git a/src/disassembler_x86.cc b/src/disassembler_x86.cc
index f70289f..646e978 100644
--- a/src/disassembler_x86.cc
+++ b/src/disassembler_x86.cc
@@ -511,6 +511,7 @@
           no_ops = true;
         }
         break;
+      case 0xB1: opcode << "cmpxchg"; has_modrm = true; store = true; break;
       case 0xB6: opcode << "movzxb"; has_modrm = true; load = true; break;
       case 0xB7: opcode << "movzxw"; has_modrm = true; load = true; break;
       case 0xBE: opcode << "movsxb"; has_modrm = true; load = true; break;