m4: define license

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/m4/m4.mk

@@ -7,6 +7,8 @@
 M4_VERSION = 1.4.16
 M4_SOURCE = m4-$(M4_VERSION).tar.bz2
 M4_SITE = $(BR2_GNU_MIRROR)/m4
+M4_LICENSE = GPLv3+
+M4_LICENSE_FILES = COPYING
 M4_CONF_ENV = gl_cv_func_gettimeofday_clobber=no
 
 ifneq ($(BR2_USE_WCHAR),y)