Add a recursive-iterative hybrid stage to attempt to reduce stack space, this

helps but not enough.

Start pulling cases out of PPC32DAGToDAGISel::Select.  With GCC 4, this function
required 8512 bytes of stack space for each invocation (GCC 3 required less
than 700 bytes).  Pulling this first function out gets us down to 8224.  More
to come :(

llvm-svn: 23647