dev-lang/ruby: fix various install issues

dev-lang/ruby: fix various install issues

Properly unbundle rdoc and bundler which we install via the gems.
Fix install path for default bundled gemspec, fixing file collisions
without FEATURES=userpriv.
Add USE flag for jit, but note that this does not fully disable jit, and
jit does not work due to issues with the .pch file generated for it.
Add missing PDEPEND on bundler since we now unbundle it properly.

Fixes: https://bugs.gentoo.org/673760
Signed-off-by: Hans de Graaff <graaff@gentoo.org>
Package-Manager: Portage-2.3.51, Repoman-2.3.11