Add mac/ios pthread_from_mach_thread_np

Allows us to get a pthread id from a match thread id.
From pthread.h [1]:

```
__API_AVAILABLE(macos(10.5), ios(2.0))
_Nullable pthread_t pthread_from_mach_thread_np(mach_port_t);
```

[1] - https://opensource.apple.com/source/libpthread/libpthread-416.40.3/pthread/pthread.h.auto.html

Author: fabiim

src/unix/bsd/apple/mod.rs

@@ -35,6 +35,8 @@ pub type shmatt_t = ::c_ushort;
 pub type sae_associd_t = u32;
 pub type sae_connid_t = u32;
 
+pub type mach_port_t = ::c_uint;
+
 deprecated_mach! {
     pub type vm_prot_t = ::c_int;
     pub type vm_size_t = ::uintptr_t;
@@ -3395,6 +3397,7 @@ extern "C" {
         name: *mut ::c_char,
         len: ::size_t,
     ) -> ::c_int;
+    pub fn pthread_from_mach_thread_np(port: ::mach_port_t) -> ::pthread_t;
     pub fn pthread_get_stackaddr_np(thread: ::pthread_t) -> *mut ::c_void;
     pub fn pthread_get_stacksize_np(thread: ::pthread_t) -> ::size_t;
     pub fn pthread_condattr_setpshared(