The FuzzAssemble* tests rely on two CSA functions which are relatively big. And
with the --enable-slow-asserts flag they get so big that the register
allocator's memory consumption becomes a problem. Let's just override this flag.

Bug: v8:7819, v8:6848, v8:7842
Change-Id: I95db59b9c788aa665d04339892b2e0b5d92d9a89
Reviewed-on: https://chromium-review.googlesource.com/1093315Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#53779}