For 5.7 the copyright header is different.

From ad32de7f181acaffaba78d5c3d9e5aa6b84a741c Mon Sep 17 00:00:00 2001
From: David Matthews <dm@prolingua.co.uk>
Date: Sun, 7 Apr 2019 13:41:33 +0100
Subject: [PATCH] Remove FFI_SYSV from abi table for X86/64 Unix.  It appears
 that this has been removed in upstream versions of libffi and causes problems
 when building using the system libffi.

---
 libpolyml/polyffi.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/libpolyml/polyffi.cpp b/libpolyml/polyffi.cpp
index 5424dd84..3dc9cc7c 100644
--- a/libpolyml/polyffi.cpp
+++ b/libpolyml/polyffi.cpp
@@ -1,7 +1,7 @@
 /*
     Title:  New Foreign Function Interface

-    Copyright (c) 2015  David C.J. Matthews
+    Copyright (c) 2015, 2019  David C.J. Matthews

     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
@@ -109,7 +109,6 @@ static struct _abiTable { const char *abiName; ffi_abi abiCode; } abiTable[] =
 #elif defined(X86_WIN64)
     {"win64", FFI_WIN64},
 #elif defined(X86_ANY)
-    {"sysv", FFI_SYSV},
     {"unix64", FFI_UNIX64},
 #endif
     { "default", FFI_DEFAULT_ABI}