[Atomics] Make Atomics.compareExchange a builtin using TF

src/compiler/ppc/code-generator-ppc.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 1965 matching lines @@
       ASSEMBLE_ATOMIC_STORE_INTEGER(sth, sthx);
       break;
     case kAtomicStoreWord32:
       ASSEMBLE_ATOMIC_STORE_INTEGER(stw, stwx);
       break;
     case kAtomicExchangeInt8:
     case kAtomicExchangeUint8:
     case kAtomicExchangeInt16:
     case kAtomicExchangeUint16:
     case kAtomicExchangeWord32:
+    case kAtomicCompareExchangeInt8:
+    case kAtomicCompareExchangeUint8:
+    case kAtomicCompareExchangeInt16:
+    case kAtomicCompareExchangeUint16:
+    case kAtomicCompareExchangeWord32:
       UNREACHABLE();
       break;
     default:
       UNREACHABLE();
       break;
   }
   return kSuccess;
 }  // NOLINT(readability/fn_size)
 
 
@@ skipping 592 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8