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

[Matt Arsenault via cfe-commits]

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@@ -127,11 +127,7 @@ template <typename T> constexpr vector<T, 4> lit_impl(T NDotL, T NDotH, T M) {
 }
 
 template <typename T> constexpr T faceforward_impl(T N, T I, T Ng) {
-#if (__has_builtin(__builtin_spirv_faceforward))
-  return __builtin_spirv_faceforward(N, I, Ng);
-#else
   return select(dot(I, Ng) < 0, N, -N);
-#endif
 }
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arsenm wrote:

Should not be done in this patch 

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