[clang] [llvm] [SPIRV][HLSL] map lerp to Fmix (PR #88976)

[Vyacheslav Levytskyy via cfe-commits]

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@@ -58,4 +58,6 @@ let TargetPrefix = "spv" in {
       Intrinsic<[ llvm_ptr_ty ], [llvm_i8_ty], [IntrWillReturn]>;
   def int_spv_all : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_any_ty]>;
   def int_spv_any : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_any_ty]>;
+  def int_spv_lerp : Intrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty, LLVMMatchType<0>,LLVMMatchType<0>], 
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VyacheslavLevytskyy wrote:

Should we insert a description of the newly added intrinsic into docs/SPIRVUsage.rst as a part of the same PR? What do you think @michalpaszkowski ?

https://github.com/llvm/llvm-project/pull/88976