[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 7127472361bdd0781dc86e6a2bbb48ef62032bf2..eb8f13d81109e01119c2c55b3f69935e10075eeb 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -2115,6 +2115,10 @@ void InstructionSelector::VisitAtomicStore(Node* node) {
 
 void InstructionSelector::VisitAtomicExchange(Node* node) { UNIMPLEMENTED(); }
 
+void InstructionSelector::VisitAtomicCompareExchange(Node* node) {
+  UNIMPLEMENTED();
+}
+
 // static
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {