Mark host_platform_repo rule as local

So that it won't be vendored

host/extension.bzl

diff --git a/host/extension.bzl b/host/extension.bzl
index 13ae09a..a888a20 100644
--- a/host/extension.bzl
+++ b/host/extension.bzl
@@ -54,6 +54,7 @@
 file contains a single <code>HOST_CONSTRAINTS</code> variable, which is a
 list of strings, each of which is a label to a <code>constraint_value</code>
 for the host platform.""",
+    local = True,
 )
 
 def _host_platform_impl(module_ctx):