Node now requires gcc >=6.3, and we do not test on gcc <5.4 any more.
Thus remove a special case for gcc <5.

R=machenbach@chromium.org

Bug: v8:9686
Change-Id: Ifffddec611c15b704aa292a65e87cd770d85ea7b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1786283Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63572}