Rework well_known_protos attr, and some other fixes
diff --git a/bazel/generate_cc.bzl b/bazel/generate_cc.bzl
index d05509f..7fffb58 100644
--- a/bazel/generate_cc.bzl
+++ b/bazel/generate_cc.bzl
@@ -57,7 +57,7 @@
 
   return struct(files=set(out_files))
 
-generate_cc = rule(
+_generate_cc = rule(
     attrs = {
         "srcs": attr.label_list(
             mandatory = True,
@@ -90,3 +90,9 @@
     output_to_genfiles = True,
     implementation = generate_cc_impl,
 )
+
+def generate_cc(well_known_protos, **kwargs):
+  if well_known_protos:
+    _generate_cc(well_known_protos="@com_google_protobuf//:well_known_protos", **kwargs)
+  else:
+    _generate_cc(**kwargs)