nit

Co-authored-by: lcnr <rust@lcnr.de>

compiler/rustc_symbol_mangling/src/v0.rs

@@ -651,6 +651,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
                             .builtin_deref(true)
                             .expect("tried to dereference on non-ptr type")
                             .ty;
+                        // FIXME: add an assert that we only do this for valtrees.
                         let dereferenced_const = self.tcx.mk_ct_from_kind(ct.kind(), pointee_ty);
                         self = dereferenced_const.print(self)?;
                     }