environ on macos uses directly libc which has the correct signature.

Author: devnexen

std/src/sys/unix/os.rs

@@ -472,10 +472,7 @@ impl Iterator for Env {
 
 #[cfg(target_os = "macos")]
 pub unsafe fn environ() -> *mut *const *const c_char {
-    extern "C" {
-        fn _NSGetEnviron() -> *mut *const *const c_char;
-    }
-    _NSGetEnviron()
+    libc::_NSGetEnviron() as *mut *const *const c_char
 }
 
 #[cfg(not(target_os = "macos"))]