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

(cherry picked from commit d1b5e5bdebc954e149feecd745bdf9e4d5e2a668)
CB-6212 iOS: fix warnings compiled under arm64 64-bit

(cherry picked from commit d1b5e5bdebc954e149feecd745bdf9e4d5e2a668)
RTC#55592 add IBM-MODIFICATIONS file