libarchive: do not extract unsafe symlinks unless $EXTRACT_UNSAFE_SYMLINKS=1

function                                             old     new   delta
unsafe_symlink_target                                  -     147    +147
unzip_main                                          2711    2732     +21
copy_file                                           1657    1678     +21
tar_main                                             999     971     -28
data_extract_all                                    1038     984     -54
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 2/2 up/down: 189/-82)           Total: 107 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/copy_file.c b/libbb/copy_file.c
index 23c0f83..be90066 100644
--- a/libbb/copy_file.c
+++ b/libbb/copy_file.c
@@ -371,7 +371,10 @@
 			int r = symlink(lpath, dest);
 			free(lpath);
 			if (r < 0) {
-				bb_perror_msg("can't create symlink '%s'", dest);
+				/* shared message */
+				bb_perror_msg("can't create %slink '%s' to '%s'",
+					"sym", dest, lpath
+				);
 				return -1;
 			}
 			if (flags & FILEUTILS_PRESERVE_STATUS)