mman add MAP_CONCEAL mmap flag for openbsd

Author: devnexen

src/sys/mman.rs

@@ -140,6 +140,9 @@ libc_bitflags!{
         MAP_NOCACHE;
         #[cfg(any(target_os = "ios", target_os = "macos"))]
         MAP_JIT;
+        /// Pages will be discarded in the core dumps.
+        #[cfg(target_os = "openbsd")]
+        MAP_CONCEAL;
     }
 }