Mark extension as reproducible (#1416)

Author: fmeum

foreign_cc/extensions.bzl

@@ -1,5 +1,6 @@
 """Entry point for extensions used by bzlmod."""
 
+load("@bazel_features//:features.bzl", "bazel_features")
 load("//foreign_cc:repositories.bzl", "rules_foreign_cc_dependencies")
 load("//toolchains:prebuilt_toolchains.bzl", "prebuilt_toolchains")
 
@@ -44,6 +45,11 @@ def _init(module_ctx):
         register_toolchains = False,
     )
 
+    if bazel_features.external_deps.extension_metadata_has_reproducible:
+        return module_ctx.extension_metadata(reproducible = True)
+    else:
+        return None
+
 tools = module_extension(
     implementation = _init,
     tag_classes = {