[llvm] [RISCV] Add experimental support for making i32 a legal type on RV64 in SelectionDAG. (PR #70357)

[Alex Bradbury via llvm-commits]

https://github.com/asb approved this pull request.

LGTM. I think duplicating the tests to avoid an overabundance of CHECK lines in the existing ones was a good way to handle this. I've also tested this doesn't seem to indicate any compile or runtime failures on the GCC torture suite when enabled.

https://github.com/llvm/llvm-project/pull/70357