buildroot

libcoap: new package

Signed-off-by: Joris Lijssens <joris.lijssens@gmail.com>
[Thomas:
 - Adjust license: it is "GPLv2+ or BSD-2c" and not "GPLv2, BSD-2c"
 - Add the COPYING file to the license files, since it indicates
   explictly that the license is GPLv2+ or BSD-2c.
 - Remove the --with-shared configure options, which doesn't exist.
 - Use LIBCOAP_AUTORECONF = YES instead of calling the autogen.sh script
   manually.
 - Add patch to fix build with old gcc versions.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>