package/x11r7/libxcb: add LIBXCB_CPE_ID_VENDOR

cpe:2.3:a:x:libxcb is a valid CPE identifier for this package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Ax%3Alibxcb

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/x11r7/libxcb/libxcb.mk

@@ -9,6 +9,7 @@ LIBXCB_SOURCE = libxcb-$(LIBXCB_VERSION).tar.xz
 LIBXCB_SITE = http://xcb.freedesktop.org/dist
 LIBXCB_LICENSE = MIT
 LIBXCB_LICENSE_FILES = COPYING
+LIBXCB_CPE_ID_VENDOR = x
 
 LIBXCB_INSTALL_STAGING = YES