Pull c10 headers directly from PyTorch internally, not from the c10 mirror

Previously, both internal and external worlds got ExecuTorch's pinned version of PyTorch. Now external is the same, but internal gets its monorepo behavior. PyTorch guarantees backward compatibility (i.e., not breaking the builds of existing PyTorch users), so our ExecuTorch code that works with pinned PyTorch should also automatically work with internal PyTorch. (bc breaks will be difficult, but that's inherent to bc breaks.)

Differential Revision: [D76832520](https://our.internmc.facebook.com/intern/diff/D76832520/)

[ghstack-poisoned]

Author: swolchok

runtime/core/portable_type/c10/c10/targets.bzl

@@ -49,43 +49,6 @@ def define_common_targets():
     The directory containing this targets.bzl file should also contain both
     TARGETS and BUCK files that call this function.
     """
-    runtime.cxx_library(
-        name = "c10",
-        header_namespace = "c10",
-        exported_headers = [
-            "macros/Export.h",
-            "macros/Macros.h",
-            "util/BFloat16.h",
-            "util/BFloat16-inl.h",
-            "util/BFloat16-math.h",
-            "util/Half.h",
-            "util/Half-inl.h",
-            "util/TypeSafeSignMath.h",
-            "util/bit_cast.h",
-            "util/complex.h",
-            "util/complex_math.h",
-            "util/complex_utils.h",
-            "util/floating_point_utils.h",
-            "util/irange.h",
-        ],
-        exported_preprocessor_flags = [
-            "-DC10_USING_CUSTOM_GENERATED_MACROS",
-        ] + ([] if runtime.is_oss else [
-            "-DC10_USE_GLOG",
-            "-DC10_USE_MINIMAL_GLOG",
-        ]),
-        visibility = [
-            "//executorch/...",
-            "@EXECUTORCH_CLIENTS",
-        ],
-        deps = select({
-            "DEFAULT": [],
-            # Half-inl.h depends on vec_half.h from ATen, but only when building for x86.
-            "ovr_config//cpu:x86_64": [
-                ":aten_headers_for_executorch",
-            ],
-        }),
-    )
 
     runtime.cxx_library(
         name = "aten_headers_for_executorch",
@@ -118,3 +81,51 @@ def define_common_targets():
         fbcode_exported_preprocessor_flags = get_preprocessor_flags(is_fbcode=True)
         + ([] if runtime.is_oss else ["-DET_USE_PYTORCH_HEADERS"]),
     )
+
+    if runtime.is_oss:
+        runtime.cxx_library(
+            name = "c10",
+            header_namespace = "c10",
+            exported_headers = [
+                "macros/Export.h",
+                "macros/Macros.h",
+                "util/BFloat16.h",
+                "util/BFloat16-inl.h",
+                "util/BFloat16-math.h",
+                "util/Half.h",
+                "util/Half-inl.h",
+                "util/TypeSafeSignMath.h",
+                "util/bit_cast.h",
+                "util/complex.h",
+                "util/complex_math.h",
+                "util/complex_utils.h",
+                "util/floating_point_utils.h",
+                "util/irange.h",
+            ],
+            exported_preprocessor_flags = [
+                "-DC10_USING_CUSTOM_GENERATED_MACROS",
+            ] + ([] if runtime.is_oss else [
+                "-DC10_USE_GLOG",
+                "-DC10_USE_MINIMAL_GLOG",
+            ]),
+            visibility = [
+                "//executorch/...",
+                "@EXECUTORCH_CLIENTS",
+            ],
+            deps = select({
+                "DEFAULT": [],
+                # Half-inl.h depends on vec_half.h from ATen, but only when building for x86.
+                "ovr_config//cpu:x86_64": [
+                    ":aten_headers_for_executorch",
+                ],
+            }),
+        )
+    else:
+        runtime.cxx_library(
+            name = "c10",
+            exported_deps = [":aten_headers_for_executorch"],
+            visibility = [
+                "//executorch/...",
+                "@EXECUTORCH_CLIENTS",
+            ],
+        )