[MSP430] Add MC layer

Reapply r346374 with the fixes for modules build.

Original summary:

This change implements assembler parser, code emitter, ELF object writer
and disassembler for the MSP430 ISA.  Also, more instruction forms are added
to the target description.

Patch by Michael Skvortsov!

llvm-svn: 346948
diff --git a/llvm/lib/Object/ELF.cpp b/llvm/lib/Object/ELF.cpp
index da56d97..2edab0b 100644
--- a/llvm/lib/Object/ELF.cpp
+++ b/llvm/lib/Object/ELF.cpp
@@ -139,6 +139,13 @@
       break;
     }
     break;
+  case ELF::EM_MSP430:
+    switch (Type) {
+#include "llvm/BinaryFormat/ELFRelocs/MSP430.def"
+    default:
+      break;
+    }
+    break;
   default:
     break;
   }