In C to WASM stubs, when number of parameters is more than 5, or
anything requires stack arguments, current linkage is faulty
because of missing STACK_SHADOW_WORDS

Drive-by: Also cleanup s390 code which is not supported anymore.

R=joransiu@ca.ibm.com

Change-Id: I7405c32fd94e158e6868f9ce7d4390c995078dbb
Reviewed-on: https://chromium-review.googlesource.com/c/1257269Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#56352}