Add patch with which the tarball was generated

0001-Ensure-libffi.map-is-generated.patch

+From 77e130c1e2f2879ffe9b7add0873101c50208d1a Mon Sep 17 00:00:00 2001
+From: Ben Gamari <ben@smart-cactus.org>
+Date: Mon, 2 Oct 2017 09:45:05 -0400
+Subject: [PATCH] Ensure libffi.map is generated
+
+---
+ configure.ac | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/configure.ac b/configure.ac
+index d155a6d..f3162d5 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -383,6 +383,6 @@ test -d src/$TARGETDIR || mkdir src/$TARGETDIR
+ 
+ AC_CONFIG_LINKS(include/ffitarget.h:src/$TARGETDIR/ffitarget.h)
+ 
+-AC_CONFIG_FILES(include/Makefile include/ffi.h Makefile testsuite/Makefile man/Makefile doc/Makefile libffi.pc)
++AC_CONFIG_FILES(include/Makefile include/ffi.h Makefile testsuite/Makefile man/Makefile doc/Makefile libffi.pc libffi.map)
+ 
+ AC_OUTPUT
+-- 
+2.11.0
+