Auto merge of #2624 - rtzoeller:umount_nofollow, r=Amanieu
Auto merge of #2624 - rtzoeller:umount_nofollow, r=Amanieu

Define UMOUNT_NOFOLLOW on Linux-like platforms

Requested-by: https://github.com/nix-rust/nix/issues/1631

rust-lang/libc,rust-lang/libc,rust-lang/libc