Add the GPU rigid body pipeline from https://github.com/erwincoumans/experiments as a Bullet 3.x preview for Bullet 2.80

Extras/RigidBodyGpuPipeline/opencl/gpu_rigidbody_pipeline2/CLPhysicsDemo.h

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+/*
+Copyright (c) 2012 Advanced Micro Devices, Inc.  
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+//Originally written by Erwin Coumans
+
+#ifndef CL_PHYSICS_DEMO_H
+#define CL_PHYSICS_DEMO_H
+
+class Win32OpenGLWindow;
+
+struct CLPhysicsDemo
+{
+	Win32OpenGLWindow* m_renderer;
+
+	int m_numCollisionShapes;
+
+	int m_numPhysicsInstances;
+
+	struct InternalData* m_data;
+	
+	CLPhysicsDemo(Win32OpenGLWindow*	renderer);
+	
+	virtual ~CLPhysicsDemo();
+
+	//btOpenCLGLInteropBuffer*	m_interopBuffer;
+	
+	void	init(int preferredDevice, int preferredPlatform, bool useInterop);
+	
+	void	setupInterop();
+
+	int		registerCollisionShape(const float* vertices, int strideInBytes, int numVertices, const float* scaling);
+
+	int		registerPhysicsInstance(float mass, const float* position, const float* orientation, int collisionShapeIndex, void* userPointer);
+
+	void	writeVelocitiesToGpu();
+	void	writeBodiesToGpu();
+
+	void	cleanup();
+
+	void	stepSimulation();
+};
+
+#endif//CL_PHYSICS_DEMO_H