gnu: pipewire: Fix build with GCC 10.

* gnu/packages/patches/pipewire-0.2.7-fno-common.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/linux.scm (pipewire)[source]: Use it.

Signed-off-by: Guillaume Le Vaillant <glv@posteo.net>

gnu/local.mk

@@ -1567,6 +1567,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/pinball-system-ltdl.patch		\
   %D%/packages/patches/pingus-boost-headers.patch		\
   %D%/packages/patches/pingus-sdl-libs-config.patch		\
+  %D%/packages/patches/pipewire-0.2.7-fno-common.patch		\
   %D%/packages/patches/pixman-CVE-2016-5296.patch		\
   %D%/packages/patches/pjproject-correct-the-cflags-field.patch \
   %D%/packages/patches/pjproject-fix-pkg-config-ldflags.patch	\

gnu/packages/linux.scm

@@ -55,6 +55,7 @@
 ;;; Copyright © 2021 Ivan Gankevich <i.gankevich@spbu.ru>
 ;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
 ;;; Copyright © 2021 Guillaume Le Vaillant <glv@posteo.net>
+;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -7845,7 +7846,8 @@ types and interfaces and translates so that the X server can use them.")
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "1q5wrqnhhs6r49p8yvkw1pl0cnsd4rndxy4h5lvdydwgf1civcwc"))))
+                "1q5wrqnhhs6r49p8yvkw1pl0cnsd4rndxy4h5lvdydwgf1civcwc"))
+              (patches (search-patches "pipewire-0.2.7-fno-common.patch"))))
     (build-system meson-build-system)
     (arguments
      '(#:configure-flags '("-Dsystemd=false")))

gnu/packages/patches/pipewire-0.2.7-fno-common.patch

@@ -0,0 +1,51 @@
+Fixes 'multiple definition errors' when building with GCC 10+
+
+From: https://bugs.gentoo.org/710796
+Originally from: https://gitlab.freedesktop.org/pipewire/pipewire/-/commit/a62e41e
+and https://gitlab.freedesktop.org/pipewire/pipewire/-/commit/7a976c7
+
+--- a/spa/plugins/bluez5/a2dp-codecs.h
++++ b/spa/plugins/bluez5/a2dp-codecs.h
+@@ -284,15 +284,15 @@
+         }
+ }
+ 
+-const a2dp_sbc_t bluez_a2dp_sbc;
++extern const a2dp_sbc_t bluez_a2dp_sbc;
+ #if ENABLE_MP3
+-const a2dp_mpeg_t bluez_a2dp_mpeg;
++extern const a2dp_mpeg_t bluez_a2dp_mpeg;
+ #endif
+ #if ENABLE_AAC
+-const a2dp_aac_t bluez_a2dp_aac;
++extern const a2dp_aac_t bluez_a2dp_aac;
+ #endif
+ #if ENABLE_APTX
+-const a2dp_aptx_t bluez_a2dp_aptx;
++extern const a2dp_aptx_t bluez_a2dp_aptx;
+ #endif
+ 
+ #endif
+--- a/spa/plugins/bluez5/bluez5-monitor.c
++++ b/spa/plugins/bluez5/bluez5-monitor.c
+@@ -75,7 +75,7 @@
+ 	struct spa_list transport_list;
+ };
+ 
+-struct spa_handle_factory spa_a2dp_sink_factory;
++extern struct spa_handle_factory spa_a2dp_sink_factory;
+ 
+ static void fill_item(struct spa_bt_monitor *this, struct spa_bt_transport *transport,
+ 		struct spa_pod **result, struct spa_pod_builder *builder)
+--- a/spa/plugins/bluez5/meson.build
++++ b/spa/plugins/bluez5/meson.build
+@@ -1,7 +1,8 @@
+ 
+ bluez5_sources = ['plugin.c',
+ 		  'a2dp-sink.c',
+-                  'bluez5-monitor.c']
++		  'a2dp-codecs.c',
++		  'bluez5-monitor.c']
+ 
+ bluez5lib = shared_library('spa-bluez5',
+ 	bluez5_sources,