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,
+)