add the cpp target (#21164)

The issue is related to cpp codegen, the previous test doesn't test cpp backend, which will join into the megatest.

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/cpp/t12946.nim b/tests/cpp/t12946.nim
index cf6bf5cfc..79cd56251 100644
--- a/tests/cpp/t12946.nim
+++ b/tests/cpp/t12946.nim
@@ -1,3 +1,7 @@
+discard """
+  targets: "c cpp"
+"""
+
 import std/atomics
 type Futex = distinct Atomic[int32]