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

src/llvm2ice.cpp

Index: src/llvm2ice.cpp
diff --git a/src/llvm2ice.cpp b/src/llvm2ice.cpp
index 2b323f7c8da4c3bc9e7ac1840d7b32a80f2332db..c3a98dfed6b2d13a06f6dbeeb054d700990864ab 100644
--- a/src/llvm2ice.cpp
+++ b/src/llvm2ice.cpp
@@ -599,8 +599,6 @@ private:
       }
     }
     if (Call->getNumArgs() + 1 != I->NumTypes) {
-      std::cerr << "Call->getNumArgs() " << (int)Call->getNumArgs()
-                << " I->NumTypes " << (int)I->NumTypes << "\n";
       report_fatal_error("Mismatched # of args.");
     }
     for (size_t i = 1; i < I->NumTypes; ++i) {