ia64: Work around miscompilation and fix build on ia64's gcc-10 and later

Needed since gcc-10 enabled -fno-common by default.

[In use in Gentoo since gcc-10, no problems observed.
Also discussed with and reviewed by Jessica Clarke from
Debian. Andreas]

Bug: https://bugs.gentoo.org/723268


Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Sergei Trofimovich <slyich@gmail.com>
Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>