Add SPDX-License-Identifier for files that already specify license

This is a step towards REUSE compliance. Third-party files that we do
not otherwise edit (git.mk, m4/attributes.m4) are excluded here.

Signed-off-by: Simon McVittie <smcv@collabora.com>

bind-mount.c

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

bind-mount.h

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

bubblewrap.c

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

network.c

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

network.h

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

tests/libtest.sh

@@ -4,6 +4,7 @@
 # Add non-bubblewrap-specific code to libtest-core.sh instead.
 #
 # Copyright (C) 2017 Colin Walters <walters@verbum.org>
+# SPDX-License-Identifier: LGPL-2.0-or-later
 #
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public

utils.c

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public

utils.h

@@ -1,5 +1,6 @@
 /* bubblewrap
  * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public