lang/swi-pl: Add explicit readline dependency (D29353)

This unbreaks the build when using devel/samurai.

It previously got it through ninja->python->readline.

===>  Building package for swi-pl-8.2.3_1
pkg-static: Unable to access file /wrkdirs/usr/ports/lang/swi-pl/work/stage/usr/local/lib/swipl/doc/packages/readline.html:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/lang/swi-pl/work/stage/usr/local/lib/swipl/lib/amd64-freebsd/readline4pl.so:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/lang/swi-pl/work/stage/usr/local/lib/swipl/library/readline.pl:No such file or directory
*** Error code 1

http://package18.nyi.freebsd.org/data/122amd64-default-foo/2021-04-04_07h37m38s/logs/errors/swi-pl-8.2.3_1.log

PR:		254678

lang/swi-pl/Makefile

@@ -2,7 +2,7 @@
 
 PORTNAME=	swi-pl
 DISTVERSION=	8.2.3
-PORTREVISION=	1
+PORTREVISION=	2
 CATEGORIES=	lang
 MASTER_SITES=	http://www.swi-prolog.org/download/stable/src/
 DISTNAME=	swipl-${DISTVERSION}
@@ -20,8 +20,8 @@ LIB_DEPENDS=	libpcre.so:devel/pcre \
 		libossp-uuid.so:misc/ossp-uuid \
 		libyaml.so:textproc/libyaml
 
-USES=		compiler:c11 libedit cmake libarchive pathfix pkgconfig \
-		shebangfix ssl
+USES=		cmake compiler:c11 libarchive libedit pathfix pkgconfig \
+		readline shebangfix ssl
 USE_XORG=	ice sm x11 xext xft xinerama xpm xt
 
 OPTIONS_DEFINE=		DOCS TCMALLOC EXAMPLES XPCE GMP THREADED ODBC