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/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 3cfc800..0bd5c56 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -17,8 +17,10 @@
 // Register live intervals: Registers must be defined only once, and must be
 // defined before use.
 //
-// The machine code verifier is enabled with the command-line option
-// -verify-machineinstrs.
+// The machine code verifier is enabled from LLVMTargetMachine.cpp with the
+// command-line option -verify-machineinstrs, or by defining the environment
+// variable LLVM_VERIFY_MACHINEINSTRS to the name of a file that will receive
+// the verifier errors.
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/BitVector.h"