CB-6212 iOS: fix warnings compiled under arm64 64-bit

(cherry picked from commit 29fa80ba5dfa27f5be4e254442d72037cf3ff71e)
CB-6212 iOS: fix warnings compiled under arm64 64-bit

(cherry picked from commit 29fa80ba5dfa27f5be4e254442d72037cf3ff71e)
RTC#55592 add IBM-MODIFICATIONS file