add changes for layoutafter/layoutbefore/ingroup/layoutpass and test cases

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@174658 91177308-0d34-0410-b5e6-96231b3b80d8
fix segment ordering of elf segments

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@174659 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Add support for reading dynamic libraries.