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

lib/libshare/Makefile.am

@@ -2,6 +2,8 @@ include $(top_srcdir)/config/Rules.am
 
 DEFAULT_INCLUDES += -I$(srcdir)
 
+AM_CFLAGS += -fvisibility=hidden
+
 noinst_LTLIBRARIES = libshare.la
 
 USER_C = \

lib/libshare/nfs.c

@@ -119,7 +119,7 @@ nfs_fini_tmpfile(const char *exports, char *tmpfile)
 	return (SA_OK);
 }
 
-__attribute__((visibility("hidden"))) int
+int
 nfs_toggle_share(const char *lockfile, const char *exports,
     const char *expdir, sa_share_impl_t impl_share,
     int(*cbk)(sa_share_impl_t impl_share, char *filename))

lib/libshare/os/freebsd/nfs.c

@@ -147,7 +147,7 @@ translate_opts(const char *shareopts)
  * This function copies all entries from the exports file to "filename",
  * omitting any entries for the specified mountpoint.
  */
-__attribute__((visibility("hidden"))) int
+int
 nfs_copy_entries(char *filename, const char *mountpoint)
 {
 	int error = SA_OK;

lib/libshare/os/linux/nfs.c

@@ -400,7 +400,7 @@ nfs_add_entry(const char *filename, const char *sharepath,
  * This function copies all entries from the exports file to "filename",
  * omitting any entries for the specified mountpoint.
  */
-__attribute__((visibility("hidden"))) int
+int
 nfs_copy_entries(char *filename, const char *mountpoint)
 {
 	char *buf = NULL;