build: Don't include main in lib

For that move the error quark to a separate file.

src/fbd-error.c

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2022 Guido Günther
+ *
+ * SPDX-License-Identifier: GPL-3.0+
+ *
+ * Author: Guido Günther <agx@sigxcpu.org>
+ */
+
+#include "fbd.h"
+
+GQuark
+fbd_error_quark (void)
+{
+  static GQuark quark = 0;
+
+  if (!quark)
+    quark = g_quark_from_static_string("fbd");
+
+  return quark;
+}

src/fbd.c

@@ -17,19 +17,6 @@
 
 static GMainLoop *loop;
 
-
-GQuark
-fbd_error_quark (void)
-{
-  static GQuark quark = 0;
-
-  if (!quark)
-    quark = g_quark_from_static_string("fbd");
-
-  return quark;
-}
-
-
 static gboolean
 quit_cb (gpointer user_data)
 {

src/meson.build

@@ -12,7 +12,7 @@ fbd_enum_sources = gnome.mkenums_simple('fbd-enums',
 sources = [
   generated_dbus_sources,
   fbd_enum_sources,
-  'fbd.c',
+  'fbd-error.c',
   'fbd-dev-vibra.c',
   'fbd-dev-sound.c',
   'fbd-dev-leds.c',