[llvm] Reland "RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG" (PR #168353)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

> @sdesmalen-arm do you have an idea for a fix or are we looking at reverting again?

I had reverted it here https://github.com/llvm/llvm-project/commit/e1b08731e5d81a0483a91da5eb89b1087876b9c2 (not sure why that didn't get linked on this PR)

https://github.com/llvm/llvm-project/pull/168353