[ELF] - Simplify output section creation.

When there is no SECTION commands given, all sections are
technically orphans, but now we handle script orphans sections
and regular "orphans" sections for non-scripted case differently,
though we can handle them at one place.

Patch do that change.

Differential revision: https://reviews.llvm.org/D39045

llvm-svn: 316984