Fix filename creation when printing RCS to files.

Change-Id: I04929366496ce2ac52d96540c2d41f753b293f24
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2650209Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72409}