[turbofan] Return constant type for functions with unknown parameter count.
[turbofan] Return constant type for functions with unknown parameter count.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1221753002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29364}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh