configure: do not use '@' in version string

#0a0410dd0cb0 broke #0cc4d6352c3e. This patch fixes this, which fixes the build
of gcc/glibc/gdb manuals.

Signed-off-by: "Benoît Thébaudeau" <benoit.thebaudeau@advansee.com>

#!/bin/sh

set -e

printf "Running autoconf...\n"

autoconf -Wall --force

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