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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<tr><td><span title='2018-11-23 15:42:01 +0100'>2018-11-23</span></td><td><a href='/guix/commit/etc/guix-daemon.conf.in?id=e9926f80c6553fde50ce1fcfd38d6370f841efd2'>build: Binary tarball now populates the "current-guix" profile.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-07-15 21:59:21 +0100'>2017-07-15</span></td><td><a href='/guix/commit/etc/guix-daemon.conf.in?id=08f47d7e3e4ce2e31d8964eb42f16030859a006c'>Remove task from 'guix-daemon.conf'.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>