[core.specs] for macro spec should know :let can't go in the first position

Description

The for macro does not support :let in the first position. This was reported in CLJ-207 and a patch was produced but rejected. Since we have spec for macros now, it might be an opportunity to provide a better error message. (I think first-place let should be fine, but that's neither here nor there.)

Environment

None

Assignee

Unassigned

Reporter

lvh

Labels

Approval

Triaged

Patch

None

Affects versions

Priority

Minor
Configure