Assembler::EmitVeneers has potential quadratic behavior, which appears
as hangs on chromecrash (see the linked bug). We iterate a list of
branches (unresolved_branches_), and for each branch iterate yet another
list of branches (the label link list in
RemoveBranchFromLabelLinkChain).

Ordering decisions increase the problem, by iterating in the outer loop
in ascending pc offset order, and in the inner loop (which removes the
branch from the linked list) in descending order.

This CL mostly refactors the outer loop:

- Instead of iterating over the whole unresolved_branches_ list, iterate
only the relevant part.
- Call RemoveBranchFromLabelLinkChain in descending pc offset order.
- Keep veneer emission in ascending pc offset order.

Bug: chromium:1162080
Change-Id: I77bb3d961c1b19ef1c31e777b640b213869bc1d6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2794435
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73762}