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>

 reporter_name="Nye Liu"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

 reporter_comment=""