[llvm] [DAG] visitFREEZE - always allow freezing multiple operands (PR #145939)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Any more comments before I commit?

I've added riscv-specific handling for the insert_subvector(freeze(undef),sub,idx) regression - at this point I think I've cleaned up the notable regressions.

https://github.com/llvm/llvm-project/pull/145939