My understanding is that most of these zero-days are runtime so the above wouldn't help at all. The most recent one took advantage of Apple Wallet taking first dibs on a (virus) image and loading in the payload. Changing data structures/flags/compiler optimizations wouldn't have made a difference.
The process of going from [malicious image which gets loaded by apple wallet] to [shellcode running] depends hugely on compiler flags, memory layout, etc.
