--- libffi-3.2.1/src/closures.c	2014-11-08 21:47:24.000000000 +0900
+++ libffi-3.2.1/src/closures.c	2020-05-26 19:09:26.334088215 +0900
@@ -26,7 +26,7 @@
    DEALINGS IN THE SOFTWARE.
    ----------------------------------------------------------------------- */
 
-#if defined __linux__ && !defined _GNU_SOURCE
+#if (defined __linux__ || defined __CYGWIN__) && !defined _GNU_SOURCE
 #define _GNU_SOURCE 1
 #endif