attr: add license information

Add missing license info and file for package 'attr'

[Peter: change to '+' version of licenses]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/attr/attr.mk

@@ -9,6 +9,8 @@ ATTR_SOURCE = attr-$(ATTR_VERSION).src.tar.gz
 ATTR_SITE = http://download.savannah.gnu.org/releases/attr
 ATTR_INSTALL_STAGING = YES
 ATTR_CONF_OPT = --enable-gettext=no
+ATTR_LICENSE = GPLv2+ LGPGv2.1+
+ATTR_LICENSE_FILES = doc/COPYING doc/COPYING.LGPL
 
 # While the configuration system uses autoconf, the Makefiles are
 # hand-written and do not use automake. Therefore, we have to hack