Model example for fbcode only (#3977)

Summary:
Pull Request resolved: #3977

Resolve test failure https://www.internalfb.com/intern/test/562950092964137

Introduced by D57950299, when adding BUCK to selective build

Reviewed By: mergennachin, larryliu0820

Differential Revision: D58552651

fbshipit-source-id: 47677b8bcd1183af2e498b8032b2a427b0511a41

Author: lucylq

examples/selective_build/targets.bzl

@@ -1,4 +1,4 @@
-load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "get_oss_build_kwargs", "runtime")
+load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "get_oss_build_kwargs", "is_xplat", "runtime")
 load("@fbsource//xplat/executorch/codegen:codegen.bzl", "et_operator_library", "executorch_generated_lib")
 
 def define_common_targets():
@@ -88,7 +88,7 @@ def define_common_targets():
     # Select all ops from a given model
     # TODO(larryliu0820): Add this
 
-    if not runtime.is_oss:
+    if not runtime.is_oss and not is_xplat():
         runtime.genrule(
             name = "add_mul_model",
             outs = {"add_mul": ["add_mul.pte"]},