Issue Description:

The following code compiles + works on macOS x86_64 but not arm64:

import Foundation

let msg = "Hello Syslog from Swift"
msg.withCString { cStr in
    withVaList([cStr]) { vaList in
        vsyslog(0, "%s", vaList)
    }
}

The error on macOS arm64:

Cannot convert value of type 'CVaListPointer' to expected argument type '__darwin_va_list?' (aka 'Optional<UnsafeMutablePointer<Int8>>')

Not exactly sure why this happens, it seems like both of these two code paths (here and here) might need to be updated to support __darwin_va_list on darwin arm64.