[ELF][Writer] Add a PHDR program table entry for dynamic files.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@175951 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF][Writer] Add hash table.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@175972 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF][Writer] Fill in dynamic table entries.