The wasm compile fuzzer now generates up to four functions with
different signatures, and generates calls between them.

R=ahaas@chromium.org
CC=eholk@chromium.org

Change-Id: I94903a80c78f8463dc1dee91ccf3be33c431e25a
Reviewed-on: https://chromium-review.googlesource.com/839860
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50274}