[llvm] [RISCV] Don't construct a subtarget for function declarations in RISCVPromoteConstant. (PR #224115)

[Erich Keane via llvm-commits]

erichkeane wrote:

Commenting here because this is what I've got open, but @echristo and @dwblaikie , Aaron says I should talk to you about the build errors.  They are all a bunch of "This is a bug in DExTer" type things?  But I have no idea how to track that down/figure out what causes it.

https://github.com/llvm/llvm-project/pull/224115