Building with Gcc-10 causes error "explicit specialization in non-namespace scope".
This change fixes it.

Bug: v8:12649

Change-Id: I36b2b042b336c2dfd32ba5541fdbbdb8dc8b4fd7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3473997Reviewed-by: ji qiu <qiuji@iscas.ac.cn>
Commit-Queue: ji qiu <qiuji@iscas.ac.cn>
Cr-Commit-Position: refs/heads/main@{#79185}