sys-devel/llvm: move dev-lang/perl to BDEPEND wrt #694460
dev-lang/perl is a build time dependency of llvm, only during cross
compile it must be run by the host (CBUILD) and not the target (CHOST).
Moving it to BDEPEND solves the issue of dev-lang/perl and friends
getting pulled into the dependency graph as compile time dependencies
during cross compile. BDEPEND has been introduced in EAPI=7, so the fix
is only possible for >=llvm-9.x
Closes: https://bugs.gentoo.org/694460
Signed-off-by: Steffen Kuhn <nielson2@yandex.com>
Closes: https://github.com/gentoo/gentoo/pull/12941
Signed-off-by: Michał Górny <mgorny@gentoo.org>