http://git.savannah.gnu.org/cgit/gforth.git/commit/libffi.fs?id=87ea8a180b9fe7d3bd7d48611b4a9c5acbac4d5e

--- libffi.fs.orig	Tue Jan 26 09:39:02 2016
+++ libffi.fs	Tue Jan 26 09:39:26 2016
@@ -25,7 +25,9 @@ c-library libffi
 s" ffi" add-lib
 
 \ The ffi.h of XCode needs the following line, and it should not hurt elsewhere
+\c #ifdef __APPLE__
 \c #define MACOSX
+\c #endif
 include-ffi.h-string save-c-prefix-line \ #include <ffi.h>
 \c #include <stdio.h>
 \c static void **gforth_clist;