What year is it! This file has no reason to be written in C, and has doubly no

What year is it! This file has no reason to be written in C, and has doubly no
reason to expose a global symbol 'decodeInstruction' nor to pollute the global
scope with a bunch of external linkage entities (some of which conflict with
others elsewhere in LLVM).

This is just the initial transition to C++; more cleanups to follow.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206717 91177308-0d34-0410-b5e6-96231b3b80d8