map constraints and MCInst operands to inline asm operands. This replaces the
getMCInstOperandNum() function.
The logic to determine the constraints are not in place, so we still default to
a register constraint (i.e., "r"). Also, we no longer build the MCInst but
rather return just the opcode to get the MCInstrDesc.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164979 91177308-0d34-0410-b5e6-96231b3b80d8
