[Atomics] Make Atomics.compareExchange a builtin using TF

src/compiler/ppc/instruction-selector-ppc.cc

Index: src/compiler/ppc/instruction-selector-ppc.cc
diff --git a/src/compiler/ppc/instruction-selector-ppc.cc b/src/compiler/ppc/instruction-selector-ppc.cc
index 07faaa6356bb2a743b45ac5065e206e15a835832..181436440fa2de3f071adf302493961cef21fabd 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -2119,6 +2119,10 @@ void InstructionSelector::VisitAtomicStore(Node* node) {
 
 void InstructionSelector::VisitAtomicExchange(Node* node) { UNIMPLEMENTED(); }
 
+void InstructionSelector::VisitAtomicCompareExchange(Node* node) {
+  UNIMPLEMENTED();
+}
+
 // static
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {