lib{efi,avl,share,tpool,zfs_core,zfsbootenv,zutil}: -fvisibility=hidden

No symbols affected in libavl
No symbols affected by libtpool, but pre-ANSI declarations got purged
No symbols affected by libzfs_core
No symbols affected by libzfs_bootenv

libefi got cleaned, gained efi_debug documentation in efi_partition.h,
and removes one undocumented and unused symbol from libzfs_core:

D default_vtoc_map

libnvpair saw removal of these symbols:

D nv_alloc_nosleep_def
D nv_alloc_sleep
D nv_alloc_sleep_def
D nv_fixed_ops_def
D nvlist_hashtable_init_size
D nvpair_max_recursion

libshare saw removal of these symbols from libzfs:

T libshare_nfs_init
T libshare_smb_init
T register_fstype
B smb_shares

libzutil saw removal of these internal symbols from libzfs_core:

T label_paths
T slice_cache_compare
T zpool_find_import_blkid
T zpool_open_func
T zutil_alloc
T zutil_strdup

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12191