[llvm] [RegAlloc][RISCV] Increase the spill weight by target factor (PR #113675)

[Kai Luo via llvm-commits]

bzEq wrote:

> But I think this might actually be the same thing that the reg class weight should reflect?

  // Weight override for register pressure calculation. This is the value
  // TargetRegisterClass::getRegClassWeight() will return. The weight is in
  // units of pressure for this register class. If unset tablegen will
  // calculate a weight based on a number of register units in this register
  // class registers. The weight is per register.
  int Weight = ?;

I think it's viable. Except that regunit introduced by aliases might not be included in calculating the SpillWeight.

https://github.com/llvm/llvm-project/pull/113675