cmd/compile: fix cmd/link/internal/ld.TestDictIndex for unified IR

[mdempsky]

Delve relies on ir.Name.DictIndex being set for local variables, so that their *runtime._type can be resolved dynamically.

cmd/link/internal/ld.TestDictIndex tests that this works, but it's currently disabled for unified IR.

[gopherbot]

Change https://go.dev/cl/424735 mentions this issue: cmd/compile/internal/noder: set ir.Name.DictIndex for unified IR