VM: Fix umulh on simarm64 Windows.

runtime/vm/simulator_arm64.cc

Index: runtime/vm/simulator_arm64.cc
diff --git a/runtime/vm/simulator_arm64.cc b/runtime/vm/simulator_arm64.cc
index 4e8fde227829e2ce610d177a28560e77c516865c..3c0c99b63782a3603a1d010265de45d69c1eccdc 100644
--- a/runtime/vm/simulator_arm64.cc
+++ b/runtime/vm/simulator_arm64.cc
@@ -2261,7 +2261,8 @@ int64_t Simulator::ShiftOperand(uint8_t reg_size,
         value &= kWRegMask;
       }
       return (static_cast<uint64_t>(value) >> amount) |
-             ((value & ((1L << amount) - 1L)) << (reg_size - amount));
+             ((static_cast<uint64_t>(value) & ((1ULL << amount) - 1ULL))
+              << (reg_size - amount));
     }
     default:
       UNIMPLEMENTED();
@@ -2673,12 +2674,12 @@ void Simulator::DecodeMiscDP3Source(Instr* instr) {
     const uint64_t rm_val = get_register(rm, R31IsZR);
 #if defined(TARGET_OS_WINDOWS)
     // Visual Studio does not support __int128.
-    int64_t alu_out;
-    Multiply128(rn_val, rm_val, &alu_out);
+    uint64_t alu_out;
+    UnsignedMultiply128(rn_val, rm_val, &alu_out);
 #else
-    const __int128 res =
-        static_cast<__int128>(rn_val) * static_cast<__int128>(rm_val);
-    const int64_t alu_out = static_cast<int64_t>(res >> 64);
+    const unsigned __int128 res = static_cast<unsigned __int128>(rn_val) *
+                                  static_cast<unsigned __int128>(rm_val);
+    const uint64_t alu_out = static_cast<uint64_t>(res >> 64);
 #endif  // TARGET_OS_WINDOWS
     set_register(instr, rd, alu_out, R31IsZR);
   } else if ((instr->Bits(29, 3) == 4) && (instr->Bits(21, 3) == 5) &&