Avoiding mi_cfree on mac interpose mode

Nobody has claimed this yet.

I think you might just need to interpose malloc_default_zone too. This is what asan ends up doing, among other things (I suspect the other things it interposes are related to asan's functionality): https://github.com/llvm/llvm-project/blob/350fafabe9d3bda75e80bf077303eb5a09130b53/compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc#L85

You also can try `__attribute__((constructor(0)))` to try to get loaded earlier than with normal `__attribute__((constructor))`. Not sure if that matters for shared libs, probably not, but it can help for static linking.

This is a somewhat messy commit (includes unrelated whitespace changes, XXX comments, and doesn't reuse the existing interpose stuff) that does these and seems to work for me. https://github.com/thomcc/mimalloc/commit/52b5237028a27644ffc4e8a671d7b884a2fa7379

Unfortunately, IDK how to trigger the bad behavior that lead to you using mi_cfree in the first place, so IDK if it fixes it. That said, if you want I can PR it.

Still it's a bummer that doing this in a statically linked build isn't viable how it is on other unixes...

Start by reading compiler-rt/lib/sanitizer_common/sanitizer_malloc_mac.inc at the linked malloc_default_zone interposition code, then compare the proposed mimalloc commit 52b5237028a27644ffc4e8a671d7b884a2fa7379. Determine whether the interposition and constructor changes prevent the reported mi_cfree behavior, noting that the issue does not provide a way to reproduce it.

Written by the indexing model from the issue text.