Fix simarm and simmips builds on Mac.

runtime/vm/simulator_arm.cc

Index: runtime/vm/simulator_arm.cc
diff --git a/runtime/vm/simulator_arm.cc b/runtime/vm/simulator_arm.cc
index e06300639ec9267851eadadf76b879c6cb025e3a..b65ae800890376851eca09c0d21c08c9edec0eee 100644
--- a/runtime/vm/simulator_arm.cc
+++ b/runtime/vm/simulator_arm.cc
@@ -1174,8 +1174,10 @@ uword Simulator::CompareExchange(uword* address,
 uint32_t Simulator::CompareExchangeUint32(uint32_t* address,
                                           uint32_t compare_value,
                                           uint32_t new_value) {
-  ASSERT(sizeof(uword) == sizeof(uint32_t));
-  return CompareExchange(address, compare_value, new_value);
+  COMPILE_ASSERT(sizeof(uword) == sizeof(uint32_t));
+  return CompareExchange(reinterpret_cast<uword*>(address),
+                         static_cast<uword>(compare_value),
+                         static_cast<uword>(new_value));
 }