Revert "TargetMachine: Merge TargetMachine and LLVMTargetMachine"

Reverting to investigate layering effects of MCJIT not linking
libCodeGen but using TargetMachine::getNameWithPrefix() breaking the
lldb bots.

This reverts commit r315633.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315637 91177308-0d34-0410-b5e6-96231b3b80d8
53 files changed