fix(3p/nix/expr): use traceable_allocator for btree_map r/1530

The prior use of gc_allocator meant that the btree nodes themselves were being collected. Additionally, have Attr (contains a Value) and Bindings explicitly inherit from gc, even though Bindings is always allocated under `new (GC)`.

Detected by running under GC_ENABLE_INCREMENTAL=1.

Change-Id: Iacf13b34b5aa12e417ea87c9b46e2bf9199fdb26
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1544
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions