Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/platforms/TARGETS.v2

@@ -0,0 +1,11 @@
+# Used by open source projects to provide a simple platform setting
+
+load(":defs.bzl", "execution_platform")
+
+execution_platform(
+    name = "default",
+    cpu_configuration = "//cpu:arm64" if host_info().arch.is_aarch64 else "//cpu:x86_64",
+    os_configuration =
+        "//os:macos" if host_info().os.is_macos else "//os:windows" if host_info().os.is_windows else "//os:linux",
+    use_windows_path_separators = host_info().os.is_windows,
+)

vendor/cxx/tools/buck/prelude/platforms/defs.bzl

@@ -0,0 +1,39 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+def _execution_platform_impl(ctx: "context") -> ["provider"]:
+    constraints = dict()
+    constraints.update(ctx.attrs.cpu_configuration[ConfigurationInfo].constraints)
+    constraints.update(ctx.attrs.os_configuration[ConfigurationInfo].constraints)
+    cfg = ConfigurationInfo(constraints = constraints, values = {})
+
+    name = ctx.label.raw_target()
+    platform = ExecutionPlatformInfo(
+        label = name,
+        configuration = cfg,
+        executor_config = CommandExecutorConfig(
+            local_enabled = True,
+            remote_enabled = False,
+            use_windows_path_separators = ctx.attrs.use_windows_path_separators,
+        ),
+    )
+
+    return [
+        DefaultInfo(),
+        platform,
+        PlatformInfo(label = str(name), configuration = cfg),
+        ExecutionPlatformRegistrationInfo(platforms = [platform]),
+    ]
+
+execution_platform = rule(
+    impl = _execution_platform_impl,
+    attrs = {
+        "cpu_configuration": attrs.dep(providers = [ConfigurationInfo]),
+        "os_configuration": attrs.dep(providers = [ConfigurationInfo]),
+        "use_windows_path_separators": attrs.bool(),
+    },
+)