Return value refactor for stencilOperation()

This CL makes stencilOperation() return the computed value
rather than store it in a reference parameter.

Bug: b/200826740
Change-Id: I09f4d6fdca85a96c874e64345c3c725ab5b85982
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/66149
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>

src/Pipeline/PixelRoutine.hpp

diff --git a/src/Pipeline/PixelRoutine.hpp b/src/Pipeline/PixelRoutine.hpp
index d7212f2..855021e 100644
--- a/src/Pipeline/PixelRoutine.hpp
+++ b/src/Pipeline/PixelRoutine.hpp
@@ -68,8 +68,8 @@
 	Byte8 stencilReplaceRef();
 	void stencilTest(const Pointer<Byte> &sBuffer, const Int &x, Int sMask[4], const SampleSet &samples);
 	void stencilTest(Byte8 &value, VkCompareOp stencilCompareMode, bool isBack);
-	void stencilOperation(Byte8 &newValue, const Byte8 &bufferValue, const PixelProcessor::States::StencilOpState &ops, bool isBack, const Int &zMask, const Int &sMask);
-	void stencilOperation(Byte8 &output, const Byte8 &bufferValue, VkStencilOp operation, bool isBack);
+	Byte8 stencilOperation(const Byte8 &bufferValue, const PixelProcessor::States::StencilOpState &ops, bool isBack, const Int &zMask, const Int &sMask);
+	Byte8 stencilOperation(const Byte8 &bufferValue, VkStencilOp operation, bool isBack);
 	Float4 clampDepth(const Float4 &z);
 	Bool depthTest(const Pointer<Byte> &zBuffer, int q, const Int &x, const Float4 &z, const Int &sMask, Int &zMask, const Int &cMask);
 	void depthBoundsTest(const Pointer<Byte> &zBuffer, int q, const Int &x, Int &zMask, Int &cMask);