PPC: [Atomics] Make Atomics.exchange a builtin using TF

src/ppc/assembler-ppc.cc

Index: src/ppc/assembler-ppc.cc
diff --git a/src/ppc/assembler-ppc.cc b/src/ppc/assembler-ppc.cc
index c909cb892d1823fd5988afd150a53394f22453d0..ec6330a351d225f143506d9ffa96f755c0e76ad1 100644
--- a/src/ppc/assembler-ppc.cc
+++ b/src/ppc/assembler-ppc.cc
@@ -641,7 +641,6 @@ void Assembler::d_form(Instr instr, Register rt, Register ra,
   emit(instr | rt.code() * B21 | ra.code() * B16 | (kImm16Mask & val));
 }
 
-
 void Assembler::xo_form(Instr instr, Register rt, Register ra, Register rb,
                         OEBit o, RCBit r) {
   emit(instr | rt.code() * B21 | ra.code() * B16 | rb.code() * B11 | o | r);
@@ -1061,7 +1060,6 @@ void Assembler::lwa(Register dst, const MemOperand& src) {
 #endif
 }
 
-
 void Assembler::stb(Register dst, const MemOperand& src) {
   DCHECK(!src.ra_.is(r0));
   d_form(STB, dst, src.ra(), src.offset(), true);