No -ldl on OpenBSD.

Index: gtk/meson.build
--- gtk/meson.build.orig
+++ gtk/meson.build
@@ -50,10 +50,8 @@ deps += gtk_dep
 
 x11_dep = c_compiler.find_library('X11')
 xext_dep = c_compiler.find_library('Xext')
-dl_dep = c_compiler.find_library('dl')
 deps += x11_dep
 deps += xext_dep
-deps += dl_dep
 
 xrandr_dep = dependency('xrandr')
 deps += xrandr_dep