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/Hexagon/HexagonTargetMachine.cpp b/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
index 33439a7..7b2774f 100644
--- a/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
@@ -194,7 +194,7 @@
     // Specify the vector alignment explicitly. For v512x1, the calculated
     // alignment would be 512*alignment(i1), which is 512 bytes, instead of
     // the required minimum of 64 bytes.
-    : TargetMachine(
+    : LLVMTargetMachine(
           T,
           "e-m:e-p:32:32:32-a:0-n16:32-"
           "i64:64:64-i32:32:32-i16:16:16-i1:8:8-f32:32:32-f64:64:64-"