media-video/mpv: disable broken cross-builds with raspberry-pi in 9999

media-video/mpv: disable broken cross-builds with raspberry-pi in 9999

Upstream now uses pkg-config to determine raspberry-pi compiler
flags instead of hardcoding them. Update the ebuild accordingly.

This is nice, but Gentoo tools are broken and don't work as advertised,
see Gentoo bug 607344. Thus, disable cross-builds with raspberry-pi for
now. The required bits are in ebuild, so power users can workaround it.

Package-Manager: Portage-2.3.3, Repoman-2.3.1
Closes: https://github.com/gentoo/gentoo/pull/3718