lang/gcc11: Work around aarch64 extraction bug

Extraction fails with poudriere on aarch64 with the following error:

> SHA256 Checksum OK for gcc-11.3.0.tar.xz.

tar: Pathname can't be converted from UTF-8 to current locale.
tar: Pathname can't be converted from UTF-8 to current locale.
tar: Error exit delayed from previous errors.

Enforcing use of bsdtar works around the issue. The issue is specific to
lang/gcc11 and lang/gcc12: no other GCC port is affected.

See also bug https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246670.

PR: 271052
Reported by: Vidar Karlsen <vidar@karlsen.tech>
Reviewed by: gerald, mikael