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.

llvm-svn: 315637
diff --git a/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp b/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
index d3f24c9..aa76a96 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
@@ -143,7 +143,7 @@
                                            Optional<Reloc::Model> RM,
                                            Optional<CodeModel::Model> CM,
                                            CodeGenOpt::Level OL, bool JIT)
-    : TargetMachine(
+    : LLVMTargetMachine(
           T, computeDataLayout(TT, CPU, FS), TT, CPU, FS, Options,
           getEffectiveRelocModel(RM),
           getEffectiveCodeModel(CM, getEffectiveRelocModel(RM), JIT), OL),