The old implementation had an implicit assumption that
IsolateData::builtin_entry_table_offset is a uint12, i.e.
<4096. We're about to cross that threshold, so this patch
frees up a temp register to let the code generator handle
larger offsets.

Bug: v8:12110
Change-Id: I2c313918be4b1c4fdd2984259e5e8cc02bb24035
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3097108Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76350}