[ELF] Add Target specific Readers.

No change in functionality.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@200175 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Create Target specific Writers.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@200176 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Make changes to all the targets supported currently

X86_64,X86,PPC,Hexagon,Mips

No change in functionality.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@200177 91177308-0d34-0410-b5e6-96231b3b80d8