[ELF] - Implement --orphan-handling option.

It is PR34946.

Spec (http://man7.org/linux/man-pages/man1/ld.1.html) tells about
--orphan-handling=MODE, option where MODE can be one of four:
"place", "discard", "warn", "error".
Currently we already report orphans when -verbose given,
what becomes excessive with option implemented.

Patch stops reporting orphans when -versbose is given,
and support "place", "warn" and "error" modes.
It is not yet clear that "discard" mode is useful so it is not supported.

Differential revision: https://reviews.llvm.org/D39000

llvm-svn: 316583