Generate the test case before compilation, so that we can generate it
even if compilation crashes.
We can only do this when require_valid is true. Otherwise the test case
depends on whether the module compiles or not.

R=ahaas@chromium.org
CC=​khismet@google.com

Bug: v8:11954
Change-Id: I944e867cc7ca631bff749bd67c4b8baff1df1fa9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3074476Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76123}