[Atomics] code stubs for atomic operations

src/compiler/linkage.h

Index: src/compiler/linkage.h
diff --git a/src/compiler/linkage.h b/src/compiler/linkage.h
index 2d30545ec0d2eb301f6cffd91d82d519340861b1..c4bdbfe6e9fd3e288e8e6020e0adae7a1ae95250 100644
--- a/src/compiler/linkage.h
+++ b/src/compiler/linkage.h
@@ -364,6 +364,11 @@ class Linkage : public ZoneObject {
   // Get the location where an incoming OSR value is stored.
   LinkageLocation GetOsrValueLocation(int index) const;
 
+  // A special {Parameter} index for Stub Calls that represents context.
+  static int GetStubCallContextParamIndex(int parameter_count) {
+    return parameter_count + 0;  // Parameter (arity + 0) is special.
+  }
+
   // A special {Parameter} index for JSCalls that represents the new target.
   static int GetJSCallNewTargetParamIndex(int parameter_count) {
     return parameter_count + 0;  // Parameter (arity + 0) is special.