[Darwin][TSan] Fix false positive race report when using dispatch_apply (#204866)
Currently I have seen some false positive race reports caused by
instrumented block copy code that writes after the release-annotation.
When the block runs on another thread and reads the copied data, it
incorrectly reports this as a race.
This patch casts the block to a `void *` in order to avoid the block
copy - thus avoiding the reported race. This is safe because
`dispatch_apply` runs synchronously, so the block lives beyond all
invocations.
rdar://92286127