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/opengl_interop/btOpenCLGLInteropBuffer.h

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+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2011 Advanced Micro Devices, Inc.  http://bulletphysics.org
+
+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.
+*/
+
+///original author: Erwin Coumans
+
+#ifndef BT_OPENCL_GL_INTEROP_BUFFER_H
+#define BT_OPENCL_GL_INTEROP_BUFFER_H
+
+#include "btGlutInclude.h"
+
+#include "../basic_initialize/btOpenCLInclude.h"
+
+class btOpenCLGLInteropBuffer
+{
+
+	cl_context	m_clContext;
+	cl_command_queue	m_commandQueue;
+	cl_mem	m_buffer;
+	GLuint m_openGLVBO;
+
+public:
+	
+	btOpenCLGLInteropBuffer(cl_context	clContext, cl_command_queue	commandQueue,GLuint openGLVBO);
+	virtual ~btOpenCLGLInteropBuffer();
+
+	void	copyCL2GL();
+
+	void	copyGL2CL();
+
+	cl_mem	getCLBUffer()
+	{
+		return m_buffer;
+	}
+};
+
+#endif //BT_OPENCL_GL_INTEROP_BUFFER_H
+