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

[Philip Reames via llvm-commits]

preames wrote:

> The defaults are wrong for the allocation priorities (which RISCV also does not look like it's trying to set).

Thanks for catching this, I hadn't been aware of that mechanism.  Adding in https://github.com/llvm/llvm-project/pull/131176 though it doesn't seem to have too much effect.  

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