PPC/s390: [Atomics] Make Atomics.exchange 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 c2770b3ce8539c371cc722e1d3854f364cd1475f..7127472361bdd0781dc86e6a2bbb48ef62032bf2 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -2113,6 +2113,8 @@ void InstructionSelector::VisitAtomicStore(Node* node) {
       0, nullptr, input_count, inputs);
 }
 
+void InstructionSelector::VisitAtomicExchange(Node* node) { UNIMPLEMENTED(); }
+
 // static
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {