IWYU: missing includes for cstring in puffin

After changing from build time to run time flag for enabling puffin,
several missing includes for memcpy usage were found.

Bug: 951519
Change-Id: I06768170102ecfa9d7b2fafd6023d77314f73204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4552616


Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147334}