[clang] [llvm] [SPIRV] Add PreLegalizer pattern matching for `faceforward` (PR #139959)

[Kaitlin Peng via llvm-commits]

kmpeng wrote:

@arsenm @s-perron Would either of you like to have another look? It's ready to go in our eyes.

https://github.com/llvm/llvm-project/pull/139959