Copied from Debian.

From: Dave Martin
Subject: "rsc" doesnt exist anymore in thumb2

diff --git a/fixed.h b/fixed.h
index 4b58abf..ba4bc26 100644
--- a/fixed.h
+++ b/fixed.h
@@ -275,12 +275,25 @@ mad_fixed_t mad_f_mul_inline(mad_fixed_t x, mad_fixed_t y)
 	 : "+r" (lo), "+r" (hi)  \
 	 : "%r" (x), "r" (y))
 
+#ifdef __thumb__
+/* In Thumb-2, the RSB-immediate instruction is only allowed with a zero
+	operand.  If needed this code can also support Thumb-1 
+	(simply append "s" to the end of the second two instructions). */
+#  define MAD_F_MLN(hi, lo)  \
+    asm ("rsbs        %0, %0, #0\n\t"  \
+	 "sbc   %1, %1, %1\n\t"  \
+	 "sub   %1, %1, %2"  \
+	 : "+&r" (lo), "=&r" (hi)  \
+	 : "r" (hi)  \
+	 : "cc")
+#else /* ! __thumb__ */
 #  define MAD_F_MLN(hi, lo)  \
     asm ("rsbs	%0, %2, #0\n\t"  \
 	 "rsc	%1, %3, #0"  \
-	 : "=r" (lo), "=r" (hi)  \
+	 : "=&r" (lo), "=r" (hi)  \
 	 : "0" (lo), "1" (hi)  \
 	 : "cc")
+#endif /* __thumb__ */
 
 #  define mad_f_scale64(hi, lo)  \
     ({ mad_fixed_t __result;  \
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<div class='path'>path: <a href='/guix/log/?id=18dd5e45e4b9d7c66f386119e6578bf8b0555f63'>root</a>/<a href='/guix/log/gnu?id=18dd5e45e4b9d7c66f386119e6578bf8b0555f63'>gnu</a>/<a href='/guix/log/gnu/services?id=18dd5e45e4b9d7c66f386119e6578bf8b0555f63'>services</a>/<a href='/guix/log/gnu/services/vpn.scm?id=18dd5e45e4b9d7c66f386119e6578bf8b0555f63'>vpn.scm</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/gnu/services/vpn.scm?id=18dd5e45e4b9d7c66f386119e6578bf8b0555f63&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-07-07 10:20:28 -0400'>2021-07-07</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=02562e2f1e1b0fcc4ae17a54885f67b38fc1be46'>services: Add bitmask-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (bitmask-service-type): New variable.
* doc/guix.texi: Document it.

Co-authored-by: jgart &lt;jgart@dismail.de&gt;
</span></span></td><td>Raghav Gururajan</td></tr>
<tr><td><span title='2021-06-25 13:27:10 +0200'>2021-06-25</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=abb77e6d4c2403a3b85671001cfc4636c83ea61c'>Remove unused module imports from (gnu services vpn).</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm: Remove (gnu packages networking) and (guix utils) imports.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-06-25 00:39:32 +0200'>2021-06-25</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=66be80fabb9af0a570aee4c2e96886267a613e8e'>gnu: Add strongswan service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (&lt;strongswan-configuration&gt;): New record type.
(charon-plugins, strongswan-configuration-file)
(strongswan-shepherd-service, strongswan-service-type): New variables.
* doc/guix.tex (VPN Services): Document them all.
</span></span></td><td>Domagoj Stolfa</td></tr>
<tr><td><span title='2021-05-24 10:00:54 +0200'>2021-05-24</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=ac95609208c0afe55d68bf42993ccb9b58ad44ce'>gnu: services: Add missing wireguard related exports.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm: Export 'wireguard-peer-public-key' and
  'wireguard-peer-keep-alive'.

Signed-off-by: Guillaume Le Vaillant &lt;glv@posteo.net&gt;
</span></span></td><td>Solene Rapenne</td></tr>
<tr><td><span title='2021-04-20 14:32:53 +0200'>2021-04-20</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=3313f61e18cbb4a89ec6c980b39f8e5fcad2b890'>services: wireguard: Add keep-alive support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (&lt;wireguard-peer&gt;): Add 'keep-alive' field.
  (wireguard-configuration-file): Use it.
* doc/guix.texi (VPN Services): Document it.
</span></span></td><td>Guillaume Le Vaillant</td></tr>
<tr><td><span title='2021-02-17 10:32:15 +0100'>2021-02-17</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=43b2e440c38a39eb64088bd6c08771c060aa10fc'>services: wireguard: New service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (wireguard-peer, wireguard-configuration): New records.
(wireguard-service-type): New variable.
* doc/guix.texi (VPN Services): Document it.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-11-18 15:05:41 +0100'>2020-11-18</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=5221df34149465c5bbc1a76f83cb09f8911279f5'>gnu: vpn: Make ca, key and cert optional.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (openvpn-client-configuration)
(openvpn-server-configuration): Make ca, key an cert fields optional.
* doc/guix.texi (VPN Services): Document the change.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2020-02-19 04:08:55 +0100'>2020-02-19</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=c6c447701c9cfdeedf77224399faa9c07b12d045'>gnu: services: Add openvpn options.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (openvpn-client-configuration)
(openvpn-server-configuration): Add fast-io? and auth-user-pass options.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2020-02-19 04:08:40 +0100'>2020-02-19</span></td><td><a href='/guix/commit/gnu/services/vpn.scm?id=0372dd1a1e51e39382ee5d1aa968589b40506b8f'>gnu: services: Fix openvpn boolean fields.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vpn.scm (serialize-boolean): Do not print #t to the file.
</span></span></td><td>Julien Lepiller</td></tr>