[lld][ELF] Support non alloc sections in the Writer.

This also makes it support debugging executables built with lld.

Initial patch done by Bigcheese. This is only a revised patch to
have the functionality in the Writer.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@191032 91177308-0d34-0410-b5e6-96231b3b80d8
[lld][ELF] Group command line options for better usage

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@191033 91177308-0d34-0410-b5e6-96231b3b80d8