Patch adapted from Sage. Allows building ECL on libffi 3.3.
diff --git a/src/c/ffi.d b/src/c/ffi.d
index 8861303e..8a959c23 100644
--- a/src/c/ffi.d
+++ b/src/c/ffi.d
@@ -133,8 +133,8 @@ static struct {
 #elif defined(X86_WIN64)
   {@':win64', FFI_WIN64},
 #elif defined(X86_ANY) || defined(X86) || defined(X86_64)
-  {@':cdecl', FFI_SYSV},
-  {@':sysv', FFI_SYSV},
+  {@':cdecl', FFI_UNIX64},
+  {@':sysv', FFI_UNIX64},
   {@':unix64', FFI_UNIX64},
 #endif
 };
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<div class='path'>path: <a href='/guix/log/?id=4b28553e73cd00b7288272615a5105caf31ee692'>root</a>/<a href='/guix/log/tests?id=4b28553e73cd00b7288272615a5105caf31ee692'>tests</a>/<a href='/guix/log/tests/guix-archive.sh?id=4b28553e73cd00b7288272615a5105caf31ee692'>guix-archive.sh</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/guix-archive.sh?id=4b28553e73cd00b7288272615a5105caf31ee692&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-15 17:32:09 +0100'>2020-12-15</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=ed7d02f7c198970ce3fe94bcee47592963326446'>serialization: 'restore-file' sets canonical timestamp and permissions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-28 21:06:36 -0500'>2020-09-28</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=d8934360d2453a403b5433e71d09188e4ed23b57'>tests: Simplify shell exit status negation;</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2019-12-12 17:56:58 +0100'>2019-12-12</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=044277f610b02c3821afa0afdc2b2b140bb92cb4'>guix archive: Add '--list'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>