openntpd: fix build with musl

openntpd: fix build with musl

The recent version bump added a local sys/cdefs.h header that overrides
the internal libc provided one. But since musl does not use this header,
the __dead definition in this file is missing. Add a patch that moves
the __dead definition to sys/types.h.

Update the autoreconf reason comment. Current openntpd ships libtool
version 2.4.2 that Buildroot can safely patch.

Fixes:
http://autobuild.buildroot.net/results/2b1/2b14b7012b93f0f2bfaf9e61435dd8826217d481/
http://autobuild.buildroot.net/results/7b0/7b08c987ce200deefa21ba85a9361d818be6b206/
http://autobuild.buildroot.net/results/230/2304c4de26bd6217b79aa035be340a3c81497cbd/

Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Tested-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>