Dtype selective build: disable when not in xplat and add fail msg (#11219)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: #11090 by
@lucylq
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ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/lucylq/84/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/lucylq/84/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/lucylq/84/orig
@diff-train-skip-merge

Co-authored-by: lucylq <[email protected]>

Author: pytorchbot

examples/selective_build/targets.bzl

@@ -65,7 +65,7 @@ def define_common_targets():
         deps = [
             ":select_ops_in_dict",
         ],
-        dtype_selective_build = True,
+        dtype_selective_build = is_xplat(),
         visibility = ["//executorch/..."],
     )
 
@@ -78,7 +78,7 @@ def define_common_targets():
         deps = [
             ":select_ops_in_dict",
         ],
-        dtype_selective_build = True,
+        dtype_selective_build = is_xplat(),
         visibility = ["//executorch/..."],
     )
 

shim_et/xplat/executorch/codegen/codegen.bzl

@@ -644,8 +644,7 @@ def executorch_generated_lib(
 
     if dtype_selective_build:
         if not expose_operator_symbols and not is_xplat():
-            # TODO(T225169282): make this a fail once internal cases move to xplat.
-            warning("""
+            fail("""
                 Dtype selective build with expose_operator_symbols=False works only in xplat -
                 there are undefined symbols otherwise. Please try to use xplat, or talk to the
                 executorch team. Setting expose_operator_symbols=True is not recommended as the