X87: [Atomics] Make Atomics.store a builtin using TF.

src/x87/assembler-x87.cc

Index: src/x87/assembler-x87.cc
diff --git a/src/x87/assembler-x87.cc b/src/x87/assembler-x87.cc
index e74d77030a534b8dd76a29c10b3c2457175c39ed..5c95fcf9cd5b798ce44f0bd4dccf71ea7a72ab87 100644
--- a/src/x87/assembler-x87.cc
+++ b/src/x87/assembler-x87.cc
@@ -552,6 +552,18 @@ void Assembler::xchg(Register dst, const Operand& src) {
   emit_operand(dst, src);
 }
 
+void Assembler::xchg_b(Register reg, const Operand& op) {
+  EnsureSpace ensure_space(this);
+  EMIT(0x86);
+  emit_operand(reg, op);
+}
+
+void Assembler::xchg_w(Register reg, const Operand& op) {
+  EnsureSpace ensure_space(this);
+  EMIT(0x66);
+  EMIT(0x87);
+  emit_operand(reg, op);
+}
 
 void Assembler::adc(Register dst, int32_t imm32) {
   EnsureSpace ensure_space(this);