[llvm] [AMDGPU][SDAG] Support source modifiers on select integer operands (PR #147325)

[Chris Jackson via llvm-commits]

chrisjbris wrote:

It's possible I'm misusing shouldFoldSelectWithIdentityConstant(), but if this is the case I propose adding a similar function to TargetLowering that fulfills the intended purpose in this PR.

https://github.com/llvm/llvm-project/pull/147325