Otherwise introspection may fail because wayland-client.h cannot be found.
# CFLAGS and LDFLAGS for compiling scan program. Only needed if your app/lib
# contains GtkObjects/GObjects and you want to document signals and properties.
-GTKDOC_CFLAGS = $(GST_PLUGINS_BASE_CFLAGS) $(GST_BASE_CFLAGS)
+GTKDOC_CFLAGS = $(GST_PLUGINS_BASE_CFLAGS) $(GST_BASE_CFLAGS) $(GL_CFLAGS)
GTKDOC_LIBS = \
$(top_builddir)/gst-libs/gst/allocators/libgstallocators-@GST_API_VERSION@.la \
$(top_builddir)/gst-libs/gst/audio/libgstaudio-@GST_API_VERSION@.la \