[llvm] [PowerPC] custom constant scalar_to_vector on pwr7 (PR #109850)

[Amy Kwan via llvm-commits]

https://github.com/amy-kwan commented:

Might be a dumb question, but is it accurate to specifically say P7 in the title, when it affects more than just P7 (at least that is what it looks like from the tests)?

https://github.com/llvm/llvm-project/pull/109850