The patch fixes build failure of form:
     ../src/alpha/osf.S:298:2: error: #error "osf.S out of sync with ffi.h"
Upstream fixed the bug in a more invasive way
but didn't have releases since 3.2.1.

The patch is taken from Gentoo:
https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-libs/libffi/files/libffi-3.2.1-complex_alpha.patch

--- libffi-3.2.1/src/alpha/osf.S	2015-01-16 10:46:15.000000000 +0100
+++ libffi-3.2.1/src/alpha/osf.S	2015-01-16 10:46:24.000000000 +0100
@@ -279,6 +279,7 @@
 	.gprel32 $load_64	# FFI_TYPE_SINT64
 	.gprel32 $load_none	# FFI_TYPE_STRUCT
 	.gprel32 $load_64	# FFI_TYPE_POINTER
+	.gprel32 $load_none	# FFI_TYPE_COMPLEX
 
 /* Assert that the table above is in sync with ffi.h.  */
 
@@ -294,7 +295,8 @@
 	|| FFI_TYPE_SINT64 != 12	\
 	|| FFI_TYPE_STRUCT != 13	\
 	|| FFI_TYPE_POINTER != 14	\
-	|| FFI_TYPE_LAST != 14
+	|| FFI_TYPE_COMPLEX != 15       \
+	|| FFI_TYPE_LAST != 15
 #error "osf.S out of sync with ffi.h"
 #endif
 
b right'></td></tr></table>
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<tr><td><span title='2020-07-12 23:08:15 +0200'>2020-07-12</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=b0e7b6992f3f845e83cfbca4d700b51dba50b4d5'>gnu: Remove ".git" from "https://github/…/….git".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-17 13:34:27 +0200'>2020-06-17</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=6d164aecc8c7f2927e988f44257fa25377bf8bf4'>gnu: sbsigntools: Update to 0.9.4.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-05-20 19:38:57 +0200'>2020-05-20</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=84c983f1657e1732e1279256489dd3903ce4af33'>gnu: gnu-efi: Mark up description.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-05-20 19:38:57 +0200'>2020-05-20</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=fa876b2cd08ba46e494c6df5abd3caa2ce96dc3e'>gnu: gnu-efi: Update to 3.0.12.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-03-04 23:16:17 +0100'>2020-03-04</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=ebb7cf9e21060105d9950dd5142c0eb918083666'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-02-16 22:46:38 +0100'>2020-02-16</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=bc6c06b0bf2b7634aa0c12e4ce673c15dba51b39'>gnu: sbsigntools: Update to 0.9.3.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-01-15 00:24:28 +0100'>2020-01-15</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=bb93042c8beb881ab907fa802eefb3c4091039a2'>gnu: util-linux: Move libraries to separate output.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-12-01 00:49:16 +0100'>2019-12-01</span></td><td><a href='/guix/commit/gnu/packages/efi.scm?id=93882a9cab18134284a2635c0418d9311251a087'>gnu: gnu-efi: Update to 3.0.11.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>