[llvm] [ConstantHoisting] Add a TTI hook to prevent hoisting. (PR #69004)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

Based on feedback from @david-arm I have renamed the TTI hook to `preferToKeepConstantsAttached` so that it doesn't give the false impression the instruction has anything to hoist.

https://github.com/llvm/llvm-project/pull/69004