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,
ages/easyrpg.scm?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/easyrpg.scm'>
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<div class='path'>path: <a href='/guix/log/?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c'>root</a>/<a href='/guix/log/gnu?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c'>gnu</a>/<a href='/guix/log/gnu/packages?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c'>packages</a>/<a href='/guix/log/gnu/packages/easyrpg.scm?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c'>easyrpg.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/packages/easyrpg.scm?id=b5ed7b2201b8ca25f90a53e07edd529b4cba2d7c&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-01-18 01:14:15 +0100'>2022-01-18</span></td><td><a href='/guix/commit/gnu/packages/easyrpg.scm?id=b4dd92d38a966e14c338400b6b965bb31e4508de'>gnu: easyrpg-player: Update to 0.7.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/easyrpg.scm (easyrpg-player): Update to 0.7.0.
[inputs]: Add fluidsynth, fmt.
</span></span></td><td>Nicolas Goaziou</td></tr>
<tr><td><span title='2022-01-18 01:14:15 +0100'>2022-01-18</span></td><td><a href='/guix/commit/gnu/packages/easyrpg.scm?id=7c80c0dd082399830474b7d7fa2f1a829f5b5d91'>gnu: liblcf: Update to 0.7.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/easyrpg.scm (liblcf): Update to 0.7.0.
</span></span></td><td>Nicolas Goaziou</td></tr>
<tr><td><span title='2021-12-13 22:15:07 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/easyrpg.scm?id=e3196755e60ba7f1ed9d432e73f26a85e0c8893c'>gnu: Further simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is the result of running:

  ./pre-inst-env guix style --input-simplification=safe

and manually undoing changes on a dozen of packages to reduce
rebuilds (derivations for emacs, icecat, and libreoffice are unchanged.)
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-13 17:48:25 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/easyrpg.scm?id=8394619baceb118df92e355377fd543bb1aa501a'>gnu: Simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This commit was obtained by running:

  ./pre-inst-env guix style

without any additional argument.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-18 23:16:22 +0200'>2021-09-18</span></td><td><a href='/guix/commit/gnu/packages/easyrpg.scm?id=4e44e1c67286d89728fc6eee650ddfecd6e35366'>gnu: easyrpg-player: Add wildmidi input.</a><span class='msg-avail'>...<span class='msg-tooltip'>Suggested by moshy on #guix.

* gnu/packages/easyrpg.scm (easyrpg-player)[inputs]: Add wildmidi.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>