Auto merge of #2858 - poliorcetics:master, r=Amanieu

feat: Add `f_flags_ext` member to Apple's `statfs` structure

See the header `usr/include/sys/mount.h`:

```c
#define __DARWIN_STRUCT_STATFS64 { \
	uint32_t	f_bsize;        /* fundamental file system block size */ \
	int32_t		f_iosize;       /* optimal transfer block size */ \
	uint64_t	f_blocks;       /* total data blocks in file system */ \
	uint64_t	f_bfree;        /* free blocks in fs */ \
	uint64_t	f_bavail;       /* free blocks avail to non-superuser */ \
	uint64_t	f_files;        /* total file nodes in file system */ \
	uint64_t	f_ffree;        /* free file nodes in fs */ \
	fsid_t		f_fsid;         /* file system id */ \
	uid_t		f_owner;        /* user that mounted the filesystem */ \
	uint32_t	f_type;         /* type of filesystem */ \
	uint32_t	f_flags;        /* copy of mount exported flags */ \
	uint32_t	f_fssubtype;    /* fs sub-type (flavor) */ \
	char		f_fstypename[MFSTYPENAMELEN];   /* fs type name */ \
	char		f_mntonname[MAXPATHLEN];        /* directory on which mounted */ \
	char		f_mntfromname[MAXPATHLEN];      /* mounted filesystem */ \
	uint32_t    f_flags_ext;    /* extended flags */ \
	uint32_t	f_reserved[7];  /* For future use */ \
}
```

Author: bors

src/unix/bsd/apple/mod.rs

@@ -1051,7 +1051,8 @@ s_no_extra_traits! {
         pub f_fstypename: [::c_char; 16],
         pub f_mntonname: [::c_char; 1024],
         pub f_mntfromname: [::c_char; 1024],
-        pub f_reserved: [u32; 8],
+        pub f_flags_ext: u32,
+        pub f_reserved: [u32; 7],
     }
 
     pub struct dirent {