package/libtool: add _CPE_ID_VENDOR

cpe:2.3:a:gnu:libtool:2.4.6:* is a valid CPE identifier for this package:

 https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe:2.3:a:gnu:libtool

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
[yann.morin.1998@free.fr: drop version from reference URL]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/libtool/libtool.mk

@@ -7,6 +7,7 @@
 LIBTOOL_VERSION = 2.4.6
 LIBTOOL_SOURCE = libtool-$(LIBTOOL_VERSION).tar.xz
 LIBTOOL_SITE = $(BR2_GNU_MIRROR)/libtool
+LIBTOOL_CPE_ID_VENDOR = gnu
 
 # For the target variant, we only want to build/install libltdl
 LIBTOOL_SUBDIR = libltdl