[llvm] [llvm-size] Add -z option for Mach-O to exclude __PAGEZERO size. (PR #159574)

[Ryan Mansfield via llvm-commits]

rjmansfield wrote:

Something like `--skip-pagezero` or  `--exclude-pagezero`  maybe?  From the issue,  the counting of the 4G  __PAGEZERO segment is making the totals appear skewed and causing some confusion. The bug report calls the default output "useless" because of it. While the default output is correct, a new option that excludes would help people see the numbers are expecting to see.

https://github.com/llvm/llvm-project/pull/159574