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

Extras/RigidBodyGpuPipeline/dynamics/testbed/GL_Simplex1to4.h

@@ -0,0 +1,40 @@
+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/
+
+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.
+*/
+#ifndef GL_SIMPLEX_1TO4_H
+#define GL_SIMPLEX_1TO4_H
+
+#include "BulletCollision/CollisionShapes/btTetrahedronShape.h"
+
+#include "BulletCollision/NarrowPhaseCollision/btSimplexSolverInterface.h"
+
+///GL_Simplex1to4 is a class to debug a Simplex Solver with 1 to 4 points. 
+///Can be used by GJK.
+class GL_Simplex1to4 : public btBU_Simplex1to4
+{
+	btSimplexSolverInterface*	m_simplexSolver;
+
+	public:
+
+	GL_Simplex1to4();
+
+	void	calcClosest(btScalar* m);
+
+	void	setSimplexSolver(btSimplexSolverInterface* simplexSolver) {
+		m_simplexSolver = simplexSolver;
+	}
+
+};
+
+#endif //GL_SIMPLEX_1TO4_H