dev-libs/beignet: adjust clang version restrictions

dev-libs/beignet: adjust clang version restrictions

Unlike seemingly all versions until this point, llvm-7 has actually
increased the minor version number - meaning that the usual beignet
restriction of <clang-x.0.9999 no longer covered the whole SLOT=7. On
the plus side, there is no 7.x.9999 ebuild in the tree any more so we
can simply make this "less than 8.0.0".

Signed-off-by: Marek Szuba <marecki@gentoo.org>
Package-Manager: Portage-2.3.66, Repoman-2.3.11