Add a new SDNode ctor and InitOperands method. This allows the operands for

an SDNode to be allocated as part of the node itself, instead of being a
separate new[]'d object.  Switch HandleSDNode, LoadSDNode, and StoreSDNode
to use this mechanism.  This saves one heap allocation and free for each node
of this type that is allocated.  This reduces isel time from 2.7638 to 2.6164s
on kc++, which is a 5.6% speedup.

llvm-svn: 33877