$NetBSD: patch-configure,v 1.11 2019/10/14 11:00:56 sborrill Exp $

Link against librt on NetBSD, too.
Link-test for shm_* functions.

--- configure.orig	2018-09-19 13:43:03.000000000 +0100
+++ configure	2019-10-14 11:48:42.000000000 +0100
@@ -16264,6 +16264,11 @@
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking if posix shared mem works" >&5
 $as_echo_n "checking if posix shared mem works... " >&6; }
+case "$target_os" in
+linux*|netbsd*)
+	LIBS="-lrt  $LIBS"
+	;;
+esac
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -16284,7 +16289,7 @@
   return 0;
 }
 _ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
+if ac_fn_c_try_link "$LINENO"; then :
 
 $as_echo "#define HAVE_POSIX_SHARED_MEM 1" >>confdefs.h
 
@@ -16303,7 +16308,7 @@
 # Linux and solaris define the shm_open in -rt library.
 # This library already included in LIBS for solaris
 case "$host_os" in
-     linux*)
+     linux*|netbsd*)
         EXTRALIBS="$EXTRALIBS -lrt"
      ;;
      *)