kbuild: unify no-compiler-targets and no-sync-config-targets

Now that vdso_install does not depend on any in-tree build artifact,
it no longer needs a compiler, making no-compiler-targets the same
as no-sync-config-targets.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>