On arm64, the stack pointer has to be aligned all the time. This
alignment was not considered in the creation of the CallDescriptor in
the fuzzer and thereby caused a mismatch between the CallDescriptor and
code generator. In other words, a callee put return values in a stack
slot which was different than the stack slot where the caller expected
the return value.

With this CL we consider this alignment in the fuzzer.

R=clemensh@chromium.org

Change-Id: I8c78c24c682b7b8678c0d4d112bae99cf405b184
Reviewed-on: https://chromium-review.googlesource.com/864682Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50574}