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='2020-10-03 23:00:21 +0200'>2020-10-03</span></td><td><a href='/guix/commit/gnu/packages/antivirus.scm?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327'>gnu: clamav: Update to 0.103.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/antivirus.scm (clamav): Update to 0.103.0.
* gnu/packages/patches/clamav-system-tomsfastmath.patch: Update patch.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-19 02:19:30 +0200'>2020-07-19</span></td><td><a href='/guix/commit/gnu/packages/antivirus.scm?id=7ffec020aec9ccbc531d24e65acd93e9f3962f9f'>gnu: clamav: Update to 0.102.4.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/antivirus.scm (clamav): Update to 0.102.4.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-05-15 20:35:57 +0200'>2020-05-15</span></td><td><a href='/guix/commit/gnu/packages/antivirus.scm?id=6e9ffc3f778b43aa42c2142ec9ebbe3be4bf47cc'>gnu: clamav: End snippet in truth.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/antivirus.scm (clamav)[source]: Return #t from snippet.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-05-15 20:35:57 +0200'>2020-05-15</span></td><td><a href='/guix/commit/gnu/packages/antivirus.scm?id=d2e438d3e2fb7ba24213dccd7ee04a9dbbca96c3'>gnu: clamav: Update to 0.102.3.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/antivirus.scm (clamav): Update to 0.102.3.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>