Reland "[ELF] Enable new passmanager plugin support for LTO"

This is the orignal patch + a check that LLVM_BUILD_EXAMPLES is enabled before
adding a dependency on the 'Bye' example pass.

Original summary:

Add cli options for new passmanager plugin support to lld.

Currently it is not possible to load dynamic NewPM plugins with lld. This is an
incremental update to D76866. While that patch only added cli options for
llvm-lto2, this adds them for lld as well. This is especially useful for running
dynamic plugins on the linux kernel with LTO.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D120490