Table-driven disassembler for the X86 architecture (16-, 32-, and 64-bit

Table-driven disassembler for the X86 architecture (16-, 32-, and 64-bit
incarnations), integrated into the MC framework.

The disassembler is table-driven, using a custom TableGen backend to
generate hierarchical tables optimized for fast decode.  The disassembler
consumes MemoryObjects and produces arrays of MCInsts, adhering to the
abstract base class MCDisassembler (llvm/MC/MCDisassembler.h).

The disassembler is documented in detail in

- lib/Target/X86/Disassembler/X86Disassembler.cpp (disassembler runtime)
- utils/TableGen/DisassemblerEmitter.cpp (table emitter)

You can test the disassembler by running llvm-mc -disassemble for i386
or x86_64 targets.  Please let me know if you encounter any problems
with it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91749 91177308-0d34-0410-b5e6-96231b3b80d8