FTBFS without ext2fs attributes support

[Karlson2k]

Discovered when built on Solaris.

The suggested fix is designed to be minimally intrusive.

Alternatively two implementation could be used: one with attributes support (current) and single print of static line if attributes are not supported.

[Karlson2k]

Function chattr_get_as_str is declared in src/filemanager/cmd.h as

#ifdef ENABLE_EXT2FS_ATTR
/* chattr.c */
void chattr_cmd (WPanel * panel);
const char *chattr_get_as_str (unsigned long attr);
#endif

[Karlson2k]

I've tested the git master. Now dist could be made (tested on Debian Sid) and then mc could be built on Solaris.

However, there are a few compiler warnings, including the warning introduced by this patch:

info.c: In function ‘info_show_info’:
info.c:264:27: warning: unused variable ‘attr’ [-Wunused-variable]
  264 |             unsigned long attr;
      |                           ^~~~

The PR #189 could fix this warning as well.