flatpak: add helpers to locate flatpak installation debug dirs

The goal here is to be able to locate all of the debug directories for
active flatpak runtimes so that we can possibly decode debug libraries
from them (after verifying build-id/CRC).

src/libsysprof/sysprof-flatpak.h

@@ -0,0 +1,29 @@
+/* sysprof-flatpak.h
+ *
+ * Copyright 2019 Christian Hergert <chergert@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+gchar **sysprof_flatpak_debug_dirs (void);
+
+G_END_DECLS