Use v8_executable instead of executable for
bytecode_builtins_list_generator so that coverage link flags should be
picked up too.

Bug: v8:8068
Change-Id: I260e4de3485a78d3b3a3455441837e1a5936aa25
Reviewed-on: https://chromium-review.googlesource.com/1219326Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55787}