aix: add required changes to build with clang

Change-Id: Ie4f032c8f588b3b0e4adb9d7099cbd04ec7d50c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7120638
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1670405}
NOKEYCHECK=True
GitOrigin-RevId: 0a781a39a76d7a1da4ffbd75485daed0ec91457d