Fix simarm64 bugs on 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 65a2034d1ed8556fcfb59ba790b276dccd071478..4e8fde227829e2ce610d177a28560e77c516865c 100644
--- a/runtime/vm/simulator_arm64.cc
+++ b/runtime/vm/simulator_arm64.cc
@@ -2656,18 +2656,30 @@ void Simulator::DecodeMiscDP3Source(Instr* instr) {
     // Format(instr, "smulh 'rd, 'rn, 'rm");
     const int64_t rn_val = get_register(rn, R31IsZR);
     const int64_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);
+#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);
+#endif  // TARGET_OS_WINDOWS
     set_register(instr, rd, alu_out, R31IsZR);
   } else if ((instr->Bits(29, 2) == 0) && (instr->Bits(21, 3) == 6) &&
              (instr->Bit(15) == 0)) {
     // Format(instr, "umulh 'rd, 'rn, 'rm");
     const uint64_t rn_val = get_register(rn, R31IsZR);
     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);
+#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);
+#endif  // TARGET_OS_WINDOWS
     set_register(instr, rd, alu_out, R31IsZR);
   } else if ((instr->Bits(29, 3) == 4) && (instr->Bits(21, 3) == 5) &&
              (instr->Bit(15) == 0)) {