$NetBSD$

Fix build.

--- lib/Makefile.in.orig	2019-03-01 20:49:05.777159431 +0000
+++ lib/Makefile.in
@@ -767,7 +767,6 @@ noinst_LTLIBRARIES = libplank-internal.l
 libplank_internal_la_CFLAGS = \
 	$(AM_CFLAGS) \
 	-fPIC \
-	-fvisibility=internal \
 	$(NULL)
 
 libplank_internal_la_LDFLAGS = \