https://github.com/gtk2hs/gtk2hs/issues/276
https://bugs.gentoo.org/712988
--- a/gtk.cabal
+++ b/gtk.cabal
@@ -381,7 +381,7 @@ Library
         -- needs to be imported from this module:
         x-Signals-Import: Graphics.UI.Gtk.General.Threading
         include-dirs:   .
-        cpp-options: -U__BLOCKS__
+        cpp-options: -U__BLOCKS__ -D__attribute__(A)=
         if os(darwin) || os(freebsd)
           cpp-options: -D__attribute__(A)= -D_Nullable= -D_Nonnull=
         if !flag(deprecated)