Required to work with new lang/mujs port.

Lightly tested with some PDFs containing JavaScript.

Index: Makefile
===================================================================
RCS file: /home/cvs/ports/textproc/mupdf/Makefile,v
diff -u -p -r1.127 Makefile
--- Makefile	28 Feb 2024 09:10:55 -0000	1.127
+++ Makefile	23 Apr 2024 18:00:16 -0000
@@ -5,6 +5,7 @@ SHARED_LIBS +=  mupdf                 9.
 V =		1.23.11
 DISTNAME =	mupdf-$V-source
 PKGNAME =	mupdf-${V:S/-rc/rc/}
+REVISION =	0
 
 CATEGORIES =	textproc x11
 
@@ -76,8 +77,9 @@ CFLAGS +=	-DFZ_ENABLE_JS=0
 # js support can't be knocked out completely
 MAKE_FLAGS +=	HAVE_GLUT=No
 .else
-MAKE_FLAGS +=	ENABLE_MUJS=yes
+MAKE_FLAGS +=	ENABLE_MUJS=yes USE_SYSTEM_MUJS=yes
 WANTLIB +=	GL glut
+BUILD_DEPENDS +=lang/mujs
 LIB_DEPENDS +=	graphics/freeglut
 .endif