diff -up ./gtkgl/Makefile.am.orig ./gtkgl/Makefile.am

--- ./gtkgl/Makefile.am.orig	2018-03-22 12:45:17.380324754 +0200

+++ ./gtkgl/Makefile.am	2018-03-22 12:46:10.981897351 +0200

@@ -37,7 +37,7 @@ lib_LTLIBRARIES= libgtkgl-2.0.la

 gtkglinclude_HEADERS= gdkgl.h gtkglarea.h

 libgtkgl_2_0_la_SOURCES = gdkgl.c gtkglarea.c

 libgtkgl_2_0_la_LDFLAGS = -version-info $(GTKGL_LIBRARY_VERSION) $(export_symbols) -no-undefined

-libgtkgl_2_0_la_LIBADD = $(GTK_LIBS) $(GL_LIBS)

+libgtkgl_2_0_la_LIBADD = -lX11 $(GTK_LIBS) $(GL_LIBS)

 gtkgl-2.0.lib: libgtkgl-2.0.la gtkgl.def

 	lib -name:libgtkgl-2.0-@LT_CURRENT_MINUS_AGE@.dll -def:gtkgl.def -out:$@