Remove the code from CodeGenPrepare that moved getresult instructions

Remove the code from CodeGenPrepare that moved getresult instructions
to the block that defines their operands. This doesn't work in the
case that the operand is an invoke, because invoke is a terminator
and must be the last instruction in a block.

Replace it with support in SelectionDAGISel for copying struct values
into sequences of virtual registers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50279 91177308-0d34-0410-b5e6-96231b3b80d8