Export variant/features via soong_injection

Test: build/bazel/ci/bp2build.sh
Change-Id: If70043dc9d020d5f4a243ba4b192b99c9c7e8563
diff --git a/bp2build/conversion.go b/bp2build/conversion.go
index 96c12d3..3ab846b 100644
--- a/bp2build/conversion.go
+++ b/bp2build/conversion.go
@@ -28,6 +28,8 @@
 
 	files = append(files, newFile("product_config", "soong_config_variables.bzl", cfg.Bp2buildSoongConfigDefinitions.String()))
 
+	files = append(files, newFile("product_config", "arch_configuration.bzl", android.StarlarkArchConfigurations()))
+
 	apiLevelsContent, err := json.Marshal(android.GetApiLevelsMap(cfg))
 	if err != nil {
 		panic(err)