xtrcad has a hidden dep on mxml. Below is a possible fix.

-- Found MiniXML: /usr/local/lib/libmxml.so.0.2
[...]
/tmp/pobj/xtrkcad-5.2.2/xtrkcad-source-5.2.2GA/app/bin/svgformat.c:34:10:
fatal error: 'mxml.h' file not found
#include "mxml.h"
         ^~~~~~~~
	 1 error generated.

Index: Makefile
===================================================================
RCS file: /cvs/ports/cad/xtrkcad/Makefile,v
diff -u -p -r1.29 Makefile
--- Makefile	7 Nov 2023 14:19:21 -0000	1.29
+++ Makefile	16 Apr 2024 19:28:15 -0000
@@ -4,7 +4,7 @@ VERSION=	5.2.2
 DISTNAME=	xtrkcad-source-${VERSION}GA
 PKGNAME=	xtrkcad-${VERSION}
 CATEGORIES=	cad
-REVISION=	2
+REVISION=	3
 
 HOMEPAGE=	https://xtrkcad-fork.sourceforge.net/Wikka/HomePage
 
@@ -21,10 +21,13 @@ COMPILER=	base-clang ports-gcc
 COMPILER_LANGS=	c
 
 WANTLIB += X11 Xcomposite Xcursor Xdamage Xext Xfixes Xi Xinerama
-WANTLIB += Xrandr Xrender c fontconfig freetype m pthread z
-WANTLIB += cairo gio-2.0 glib-2.0 gobject-2.0 iconv intl zip
-WANTLIB += harfbuzz pango-1.0 pangocairo-1.0 pangoft2-1.0
-WANTLIB += gdk_pixbuf-2.0 atk-1.0 gdk-x11-2.0 gtk-x11-2.0
+WANTLIB += Xrandr Xrender atk-1.0 c cairo fontconfig freetype
+WANTLIB += gdk-x11-2.0 gdk_pixbuf-2.0 gio-2.0 glib-2.0 gobject-2.0
+WANTLIB += gtk-x11-2.0 harfbuzz iconv intl m pango-1.0 pangocairo-1.0
+WANTLIB += pangoft2-1.0 pthread z zip
+
+# force update if the statically linked mxml is updated.
+WANTLIB += mxml
 
 BUILD_DEPENDS =	devel/gettext,-tools
 
@@ -32,6 +35,7 @@ LIB_DEPENDS=	archivers/libzip \
 		devel/pango \
 		graphics/cairo \
 		graphics/gdk-pixbuf2 \
+		textproc/mxml \
 		x11/gnome/at-spi2-core \
 		x11/gtk+2