Add atomic load/store, fetch_add, fence, and is-lock-free lowering.

src/IceIntrinsics.cpp

Index: src/IceIntrinsics.cpp
diff --git a/src/IceIntrinsics.cpp b/src/IceIntrinsics.cpp
index dbf79cf11ee19d9e4a8821e4c53e60d4b6e26968..02562b53f8a2c0a4ea17b50943a9395d102146d6 100644
--- a/src/IceIntrinsics.cpp
+++ b/src/IceIntrinsics.cpp
@@ -82,7 +82,7 @@ const struct IceIntrinsicsEntry_ {
   {                                                                            \
     {                                                                          \
       { Intrinsics::AtomicStore, true }                                        \
-      , { IceType_void, Overload, IceType_i32, IceType_i32 }, 5                \
+      , { IceType_void, Overload, IceType_i32, IceType_i32 }, 4                \
     }                                                                          \
     , "nacl.atomic.store." NameSuffix                                          \
   }
@@ -199,4 +199,9 @@ Intrinsics::find(const IceString &Name) const {
   return &it->second;
 }
 
+bool Intrinsics::VerifyMemoryOrder(uint64_t Order) {
+  // There is only one memory ordering for atomics allowed right now.
+  return Order == Intrinsics::MemoryOrderSequentiallyConsistent;
+}
+
 } // end of namespace Ice