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

[Benjamin Maxwell via llvm-commits]

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

The new fixes make sense to me :+1:  
Just one more question about the initial patch: 

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