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>

# Compute sparc-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="${CT_ARCH}64"

    fi

}