bxl: Add fixme

Summary: I hit this in a real bxl script :/

Reviewed By: stepancheg

Differential Revision: D61436939

fbshipit-source-id: 7b2c8a3422d1b11bd417cbff05244b124dcb18df

app/buck2_bxl/src/bxl/starlark_defs/target_list_expr.rs

@@ -452,6 +452,9 @@ impl<'v> TargetListExpr<'v, ConfiguredTargetNode> {
             ConfiguredTargetListArg::TargetList(unpack) => {
                 let mut resolved = vec![];
 
+                // FIXME(JakobDegen): These iterations don't run in parallel, which is pretty sad.
+                // Unfortunately, that's also not easy to fix because for some reason this code
+                // prints to console
                 for item in unpack.items {
                     let unpacked = Self::unpack_literal(
                         item,