Add an ovrsource target for torch/headeronly (pytorch#157912)

Summary: no idea how this works

Test Plan:
will things just pass?

Rollback Plan:

Differential Revision: D77965219

Pull Request resolved: pytorch#157912
Approved by: https://github.com/albanD

Author: janeyx99

torch/headeronly/ovrsource_defs.bzl

@@ -0,0 +1,59 @@
+load("//arvr/tools/build_defs:oxx.bzl", "oxx_static_library")
+
+cpu_supported_platforms = [
+    "ovr_config//os:android",
+    "ovr_config//os:iphoneos",
+    "ovr_config//os:linux-x86_64",
+    "ovr_config//os:macos",
+    "ovr_config//os:windows-x86_64",
+    "ovr_config//runtime:arm64-linux-ubuntu-neon",
+    "ovr_config//os:linux-arm64",
+]
+
+def define_torch_headeronly_ovrsource(name, is_mobile):
+    if is_mobile:
+        pp_flags = ["-DC10_MOBILE=1"]
+    else:
+        pp_flags = []
+
+    oxx_static_library(
+        name = name,
+        srcs = []
+        compatible_with = cpu_supported_platforms,
+        compiler_flags = select({
+            "DEFAULT": [],
+        }),
+        include_directories = [".."],
+        preprocessor_flags = [],
+        fbobjc_compiler_flags = [],
+        public_include_directories = [".."],
+        public_preprocessor_flags = pp_flags,
+        public_raw_headers = native.glob([
+            "macros/*.h",
+        ]),
+        reexport_all_header_dependencies = False,
+        visibility = [
+            "//xplat/caffe2/torch/headeronly:torch_headeronly",
+        ],
+        deps = select({
+            "DEFAULT": [],
+        }),
+    )
+
+def define_ovrsource_targets():
+    oxx_static_library(
+        name = "torch_headeronly_ovrsource",
+        compatible_with = cpu_supported_platforms,
+        exported_deps = select({
+            "DEFAULT": [":torch_headeronly_full_ovrsource"],
+            "ovr_config//os:android": [":torch_headeronly_mobile_ovrsource"],
+            "ovr_config//os:iphoneos": [":torch_headeronly_mobile_ovrsource"],
+        }),
+        visibility = ["PUBLIC"],
+    )
+
+    """
+    Most users should use torch_headeronly_ovrsource, not these targets directly.
+    """
+    define_torch_headeronly_ovrsource("torch_headeronly_mobile_ovrsource", True)
+    define_torch_headeronly_ovrsource("torch_headeronly_full_ovrsource", False)