configure: check for GNU awk, not any awk

Building glibc requires GNU awk, not any other.

Reported-by: Han Sooloo <hansooloo@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 #!/bin/sh

 set -e

 printf "Running autoconf...\n"

 autoconf -Wall --force

 printf "Done. You may now run:\n    ./configure\n"