them as machine instructions. Directives ".set noat" and ".set at" are now
emitted only at the beginning and end of a function except in the case where
they are emitted to enclose .cpload with an immediate operand that doesn't fit
in 16-bit field or unaligned load/stores.

Also, make the following changes:
- Remove function isUnalignedLoadStore and use a switch-case statement to
  determine whether an instruction is an unaligned load or store.

- Define helper function CreateMCInst which generates an instance of an MCInst
  from an opcode and a list of operands.

llvm-svn: 153552