Incorporate cc_library_headers into mixed builds

Test: go soong tests
Test: bp2build generate & sync; mixed build libc; mixed build su (su is
      an Android.mk target that relies on converted a cc_library_headers)
Bug: 181552740
Change-Id: I9efd587970551fd41f642a208f0aa0a80e8694e0
diff --git a/cc/library.go b/cc/library.go
index 9a2b02e..0b21a08 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -426,7 +426,8 @@
 	tocFile android.OptionalPath
 
 	flagExporter
-	stripper Stripper
+	flagExporterInfo *FlagExporterInfo
+	stripper         Stripper
 
 	// For whole_static_libs
 	objects Objects