guix: Silence getent(1) invocation

Author: dongcarl

contrib/guix/guix-build

@@ -190,7 +190,7 @@ fi
 # Services database must have basic entries
 ################
 
-if ! getent services http https ftp; then
+if ! getent services http https ftp > /dev/null 2>&1; then
 cat << EOF
 ERR: Your system's C library can not find service database entries for at least
      one of the following services: http, https, ftp.