regression on -current with gst-plugins-base

gst-plugins-base doesn't build anymore on Slackware64-current:
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[218/698] Compiling C object gst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p/egl_gstglcontext_egl.c.o
FAILED: gst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p/egl_gstglcontext_egl.c.o
ccache cc -Igst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p -I. -I.. -Igst-libs -I../gst-libs -Isubprojects/gl-headers/abyss -I../subprojects/gl-headers/abyss -Isubprojects/gl-headers/wglext -I../subprojects/gl-headers/wglext -I/usr/include/gstreamer-1.0 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/gudev-1.0 -I/usr/include/libdrm -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -O3 -fvisibility=hidden -fno-strict-aliasing -DG_DISABLE_CAST_CHECKS -Wmissing-declarations -Wredundant-decls -Wundef -Wwrite-strings -Wformat -Wformat-nonliteral -Wformat-security -Winit-self -Wmissing-include-dirs -Waddress -Wno-multichar -Wvla -Wpointer-arith -Wmissing-prototypes -Wdeclaration-after-statement -O2 -fPIC -fPIC -pthread -DHAVE_CONFIG_H -DBUILDING_GST_GL -MD -MQ gst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p/egl_gstglcontext_egl.c.o -MF gst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p/egl_gstglcontext_egl.c.o.d -o gst-libs/gst/gl/libgstgl-1.0.so.0.1804.0.p/egl_gstglcontext_egl.c.o -c ../gst-libs/gst/gl/egl/gstglcontext_egl.c
In file included from ../gst-libs/gst/gl/egl/gstglcontext_egl.c:46:
../gst-libs/gst/gl/egl/../wayland/gstglwindow_wayland_egl.h:25:10: fatal error: xdg-shell-client-protocol.h: No such file or directory
25 | #include "xdg-shell-client-protocol.h"
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
[225/698] Generating GstAudio-1.0.gir with a custom command
ninja: build stopped: subcommand failed.
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