add targethandler hooks from Writer and cleanup

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173904 91177308-0d34-0410-b5e6-96231b3b80d8
change DefaultLayout to TargetLayout inside member variables

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173906 91177308-0d34-0410-b5e6-96231b3b80d8
change the function names in RelocationHelper to adhere to convention

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173908 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Add {Hexagon,PPC,X86}TargetHandler.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173909 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Use TargetRelocationHandler to apply relocations.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173911 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Remove ReferenceKinds.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@173912 91177308-0d34-0410-b5e6-96231b3b80d8