Port 42b4180d

Original Commit Message:

    The simulated C++ signature for generated code entry points should
    rely on primitive values (as opposed to ObjectPtr).

R=jkummerow@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I55c67e8d42d97b45d5b0eb878ddd6ab3cf872942
Reviewed-on: https://chromium-review.googlesource.com/c/1394755Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#58533}