Eliminate some malloc traffic by allocating vectors on the stack. Change some

Eliminate some malloc traffic by allocating vectors on the stack.  Change some
method that took std::vector<SDOperand> to take a pointer to a first operand
and #operands.

This speeds up isel on kc++ by about 3%.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29561 91177308-0d34-0410-b5e6-96231b3b80d8