Fix constexpr usage in TorchToLinalg/Pooling.cpp for MSVC. (#4086)

Fixes #4085.

Sample errors before:
https://github.com/iree-org/iree/actions/runs/13761122447/job/38477287335#step:9:7692

```
 FAILED: compiler/plugins/input/Torch/torch-mlir/CMakeFiles/iree_compiler_plugins_input_Torch_torch-mlir_ConversionPasses.objects.dir/__/__/__/__/__/third_party/torch-mlir/lib/Conversion/TorchToLinalg/Pooling.cpp.obj 
C:\ProgramData\chocolatey\bin\ccache "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\bin\Hostx64\x64\cl.exe"  /nologo /TP  -IC:\home\runner\_work\iree\iree -IC:\mnt\azure\b\095504 -IC:\home\runner\_work\iree\iree\third_party\torch-mlir\include -IC:\home\runner\_work\iree\iree\compiler\plugins\input\Torch -IC:\mnt\azure\b\095504\compiler\plugins\input\Torch -IC:\home\runner\_work\iree\iree\third_party\llvm-project\llvm\include -IC:\mnt\azure\b\095504\llvm-project\include -IC:\home\runner\_work\iree\iree\third_party\llvm-project\mlir\include -IC:\mnt\azure\b\095504\llvm-project\tools\mlir\include -IC:\home\runner\_work\iree\iree\third_party\llvm-project\lld\include -IC:\mnt\azure\b\095504\llvm-project\tools\lld\include /DWIN32 /D_WINDOWS /EHsc /Z7 /O2 /Ob1  -std:c++17 -MD /wd4996 /Zc:preprocessor /DWIN32_LEAN_AND_MEAN /DNOMINMAX /D_USE_MATH_DEFINES /D_CRT_SECURE_NO_WARNINGS /D_CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES /D_SILENCE_NONFLOATING_COMPLEX_DEPRECATION_WARNING /GR- /bigobj /W3 /wd4200 /wd4018 /wd4146 /wd4244 /wd4267 /wd4005 /wd4065 /wd4141 /wd4624 /wd4576 /wd5105 /showIncludes /Focompiler\plugins\input\Torch\torch-mlir\CMakeFiles\iree_compiler_plugins_input_Torch_torch-mlir_ConversionPasses.objects.dir\__\__\__\__\__\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp.obj /Fdcompiler\plugins\input\Torch\torch-mlir\CMakeFiles\iree_compiler_plugins_input_Torch_torch-mlir_ConversionPasses.objects.dir\ /FS -c C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1098): error C2131: expression did not evaluate to a constant
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1098): note: failure was caused by a read of a variable outside its lifetime
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1098): note: see usage of 'this'
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1098): note: the template instantiation context (the oldest one first) is
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1642): note: see reference to function template instantiation 'mlir::RewritePatternSet &mlir::RewritePatternSet::add<`anonymous-namespace'::ConvertAtenAvgPoolOp<mlir::torch::Torch::AtenAvgPool1dOp,mlir::linalg::PoolingNcwSumOp,1>,mlir::TypeConverter&,mlir::MLIRContext*&,void>(ConstructorArg,mlir::MLIRContext *&)' being compiled
        with
        [
            ConstructorArg=mlir::TypeConverter &
        ]
C:\home\runner\_work\iree\iree\third_party\llvm-project\mlir\include\mlir/IR/PatternMatch.h(1003): note: see reference to class template instantiation '`anonymous-namespace'::ConvertAtenAvgPoolOp<mlir::torch::Torch::AtenAvgPool1dOp,mlir::linalg::PoolingNcwSumOp,1>' being compiled
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(988): note: while compiling class template member function 'llvm::LogicalResult `anonymous-namespace'::ConvertAtenAvgPoolOp<mlir::torch::Torch::AtenAvgPool1dOp,mlir::linalg::PoolingNcwSumOp,1>::matchAndRewrite(OpTy,mlir::torch::Torch::AtenAvgPool1dOp::Adaptor,mlir::ConversionPatternRewriter &) const'
        with
        [
            OpTy=mlir::torch::Torch::AtenAvgPool1dOp
        ]
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1067): note: while compiling class template member function 'std::optional<llvm::LogicalResult> `anonymous-namespace'::ConvertAtenAvgPoolOp<mlir::torch::Torch::AtenAvgPool1dOp,mlir::linalg::PoolingNcwSumOp,1>::createAvgPoolValueCountIncludePadFalseCase(bool,OpTy,mlir::torch::Torch::AtenAvgPool1dOp::Adaptor,mlir::ConversionPatternRewriter &,mlir::Value,mlir::Value,mlir::Value,mlir::Type,llvm::SmallVectorImpl<T> &,llvm::SmallVectorImpl<__int64> &,llvm::SmallVectorImpl<__int64> &,llvm::SmallVector<mlir::AffineMap,6> &,llvm::SmallVector<mlir::utils::IteratorType,12> &)'
        with
        [
            OpTy=mlir::torch::Torch::AtenAvgPool1dOp,
            T=mlir::Value
        ]
C:\home\runner\_work\iree\iree\third_party\torch-mlir\lib\Conversion\TorchToLinalg\Pooling.cpp(1099): error C2039: 'getDivisorOverride': is not a member of 'mlir::torch::Torch::AtenAvgPool1dOp'
```

Author: ScottTodd

lib/Conversion/TorchToLinalg/Pooling.cpp

@@ -1084,20 +1084,27 @@ std::optional<LogicalResult> ConvertAtenAvgPoolOp<OpTy, PoolingOpTy, Dim>::
 
   PoolSizeCalculator<avgPoolDims> poolSizeCalculator(self, sumPool, rewriter,
                                                      loc);
+
+  // AtenAvgPool2/3dOp has an optional divisor_override
+  // attribute while AtenAvgPool1dOp does not.
+  // We evaluate the constexpr avgPoolDims outside of the lambda capture below
+  // for wider compiler support: https://github.com/llvm/torch-mlir/issues/4085.
+  Value poolSize = nullptr;
+  if constexpr (avgPoolDims > 1) {
+    if (!isa<Torch::NoneType>(op.getDivisorOverride().getType()))
+      poolSize = adaptor.getDivisorOverride();
+  }
+
   Value avgPool =
       rewriter
           .create<linalg::GenericOp>(
               loc, outputTensor.getType(), sumPool, outputTensor,
               /*indexingMaps=*/indexingMapsAvg,
               /*iteratorTypes=*/iteratorTypesAvg,
               [&](OpBuilder &b, Location loc, ValueRange args) {
-                auto poolSize = poolSizeCalculator.getPoolSize(
-                    b, kernelSizeIntValues, strideInts, paddingInts);
-                // AtenAvgPool2/3dOp has an optional divisor_override
-                // attribute while AtenAvgPool1dOp does not.
-                if constexpr (avgPoolDims > 1) {
-                  if (!isa<Torch::NoneType>(op.getDivisorOverride().getType()))
-                    poolSize = adaptor.getDivisorOverride();
+                if (!poolSize) {
+                  poolSize = poolSizeCalculator.getPoolSize(
+                      b, kernelSizeIntValues, strideInts, paddingInts);
                 }
                 Value divisor =
                     convertScalarToDtype(b, loc, poolSize, resultElementType);