x86/x64 port of Math.floor(x/y) to use integer division for specific divisor

src/x64/disasm-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 685 matching lines @@
     switch (regop) {
       case 2:
         mnem = "not";
         break;
       case 3:
         mnem = "neg";
         break;
       case 4:
         mnem = "mul";
         break;
+      case 5:
+        mnem = "imul";
+        break;
       case 7:
         mnem = "idiv";
         break;
       default:
         UnimplementedInstruction();
     }
     AppendToBuffer("%s%c %s",
                    mnem,
                    operand_size_code(),
                    NameOfCPURegister(rm));
@@ skipping 1129 matching lines @@
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_X64