This change makes it less likely to pick one of the registers that
are not byte addressable on ia32. This is not a correctness issue but
fixes some code size and runtime regressions.

After the change to prefer registers that are not used in hinting, it
was very likely that one of the registers that are not byte addressable
was chosen, leading to extra code in cases where the carry flags was
materialized as a real boolean value. With this change, we pick the first
register that is not used in hinting, thereby mostly using byte
addressable registers on ia32.

Change-Id: I42968cf3fd7b7db949d275c40d0afeb74b5e48c3
Reviewed-on: https://chromium-review.googlesource.com/c/1404450Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58726}