[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!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346948 91177308-0d34-0410-b5e6-96231b3b80d8
61 files changed