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='2019-06-10 23:11:07 +0200'>2019-06-10</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=226a3605d6cabeb71247a732a99d625c9cfafa74'>artwork: Update snapshot to 2f2fe74.</a><span class='msg-avail'>...</span></td><td>Diego Nicola Barbato</td></tr>
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<tr><td><span title='2019-02-10 23:25:01 +0100'>2019-02-10</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=5e6a5aeebd7b735e5d5f2eed496cc1c7e8a5b4c9'>artwork: Update snapshot to e951905.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-11-05 00:08:47 +0100'>2018-11-05</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=688d1a01e45eb1277a6337987bfd53f3fe3caaec'>artwork: Clone over HTTPS.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2015-02-12 23:43:18 +0100'>2015-02-12</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=9c09760a780d741ce39df984fc30ef728adf4d5b'>artwork: Update snapshot to GuixSD branding.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>