Now that https://crrev.com/c/728026 has landed, we can construct the
constexpr RegLists using symbolic register names instead of hard-coding
the register codes.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: I21e46aeb5e8598a56f641341bcd7cf718fe4fbf9
Reviewed-on: https://chromium-review.googlesource.com/735548Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48906}