Add linux headers 5.10.41.

Needed for kexec-tools.

Not equivalent to kernel version; kernel API is stable and does not
change. Therefore we can use any (latest) version.

sysa/linux-headers-5.10.41/patches/sed-args.patch

@@ -0,0 +1,18 @@
+SPDX-FileCopyrightText: 2021 fosslinux <fosslinux@aussies.space>
+
+SPDX-License-Identifier: GPL-2.0-only
+
+We do not have the '-E' argument in our version of sed. But it is
+functionally equivalent to '-r' (at least for this purpose).
+
+--- scripts/headers_install.shk	2021-06-01 18:48:44.732934584 +1000
++++ scripts/headers_install.sh	2021-06-01 18:48:56.954050654 +1000
+@@ -29,7 +29,7 @@
+ 	exit 1
+ fi
+ 
+-sed -E -e '
++sed -r -e '
+ 	s/([[:space:](])(__user|__force|__iomem)[[:space:]]/\1/g
+ 	s/__attribute_const__([[:space:]]|$)/\1/g
+ 	s@^#include <linux/compiler(|_types).h>@@