webkitgtk: remedy the build's confusion about the meaning of "truth"

The package could not compile because it did not know the meaning of
TRUE and FALSE [1]. So we have to make sure our build environment
provides reasonable, sensible definitions to make the build succeed.

[1] https://hydra.nixos.org/build/137292531

pkgs/development/libraries/webkitgtk/default.nix

@@ -155,6 +155,9 @@ stdenv.mkDerivation rec {
     "-DPORT=GTK"
     "-DUSE_LIBHYPHEN=OFF"
     "-DUSE_WPE_RENDERER=OFF"
+    # ensure backward compatibility with the latest version of icu:
+    # http://linuxfromscratch.org/blfs/view/svn/x/webkitgtk.html
+    "-DCMAKE_CXX_FLAGS=-DU_DEFINE_FALSE_AND_TRUE=1"
   ] ++ optionals stdenv.isDarwin [
     "-DENABLE_GRAPHICS_CONTEXT_3D=OFF"
     "-DENABLE_GTKDOC=OFF"