stack_overflow: get_stackp using MAP_STACK flag on dragonflybsd too.

Author: devnexen

library/std/src/sys/unix/stack_overflow.rs

@@ -134,9 +134,9 @@ mod imp {
         // OpenBSD requires this flag for stack mapping
         // otherwise the said mapping will fail as a no-op on most systems
         // and has a different meaning on FreeBSD
-        #[cfg(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",))]
+        #[cfg(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux", target_os = "dragonfly",))]
         let flags = MAP_PRIVATE | MAP_ANON | libc::MAP_STACK;
-        #[cfg(not(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",)))]
+        #[cfg(not(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux", target_os = "dragonfly",)))]
         let flags = MAP_PRIVATE | MAP_ANON;
         let stackp =
             mmap64(ptr::null_mut(), SIGSTKSZ + page_size(), PROT_READ | PROT_WRITE, flags, -1, 0);