Selective meta programming preparation for prim ops (#43540)

Summary:
Pull Request resolved: pytorch/pytorch#43540

selected_mobile_ops.h is generated at BUCK build time, which contains the whitelist of root operators. It's used for templated selective build when XPLAT_MOBILE_BUILD is defined.

ghstack-source-id: 111014372

Test Plan: CI and BSB

Reviewed By: ljk53

Differential Revision: D22618309

fbshipit-source-id: ddf813904892f99c3f4ae0cd14ce8b27727be5a2

aten/src/ATen/core/op_registration/op_whitelist.h

@@ -1,5 +1,10 @@
 #pragma once
 
+// TODO: unify to C10_MOBILE. In theory this header could be used in OSS.
+#ifdef XPLAT_MOBILE_BUILD
+#include <ATen/selected_mobile_ops.h>
+#endif
+
 /**
  * This header implements functionality to build PyTorch with only a certain
  * set of operators (+ dependencies) included.