add rustc build flags reflection

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/Cargo.toml

@@ -58,6 +58,7 @@ checked_ops.workspace = true
 chrono.workspace = true
 conduit-macros.workspace = true
 const-str.workspace = true
+ctor.workspace = true
 either.workspace = true
 figment.workspace = true
 http-body-util.workspace = true