protozero: Fix GN propagation of public config

The protozero_library template should propagate up a
public_config that adds the protozero/include path
to dependent targets.

Bug: 68749974
Change-Id: Ifd526c400fa58d3e42bb94ba1cef844dbb166674
diff --git a/build/proto_library.gni b/build/proto_library.gni
index 5ecc80c..c13d3f2 100644
--- a/build/proto_library.gni
+++ b/build/proto_library.gni
@@ -144,6 +144,7 @@
                            [
                              "defines",
                              "include_dirs",
+                             "public_configs",
                              "testonly",
                              "visibility",
                            ])
@@ -155,7 +156,11 @@
       configs += invoker.extra_configs
     }
 
-    public_configs = [
+    if (!defined(invoker.public_configs)) {
+      public_configs = []
+    }
+
+    public_configs += [
       "//buildtools:protobuf_gen_config",
       ":$config_name",
     ]
diff --git a/protozero/protozero_library.gni b/protozero/protozero_library.gni
index 324df6e..83818b7 100644
--- a/protozero/protozero_library.gni
+++ b/protozero/protozero_library.gni
@@ -23,6 +23,7 @@
     generator_plugin_label = "//protozero/src/protoc_plugin"
     generator_plugin_suffix = ".pbzero"
     generator_plugin_options = "wrapper_namespace=pbzero"
+    public_configs = [ "//protozero:protozero_config" ]
     forward_variables_from(invoker,
                            [
                              "defines",