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

Extras/RigidBodyGpuPipeline/build/findDirectX11.lua

@@ -0,0 +1,36 @@
+function findDirectX11()
+		local dx11path = os.getenv("DXSDK_DIR")
+		if (dx11path) then
+			local filepath = string.format("%s%s",dx11path,"Include/D3D11.h")
+			headerdx11 = io.open(filepath, "r")
+			if (headerdx11) then
+				 printf("Found DX11: '%s'", filepath)
+				return true
+			end
+		end
+		return false
+	end
+
+function initDirectX11()
+	configuration {}
+	
+	local dx11path = os.getenv("DXSDK_DIR")
+			defines { "ADL_ENABLE_DX11"}
+			includedirs {"$(DXSDK_DIR)/include"}
+	
+		configuration "x32"
+			libdirs {"$(DXSDK_DIR)/Lib/x86"}
+		configuration "x64"
+			libdirs {"$(DXSDK_DIR)/Lib/x64"}
+		configuration {}
+		links {"d3dcompiler",
+					"dxerr",
+					"dxguid",
+					"d3dx9",
+					"d3d9",
+					"winmm",
+					"comctl32",
+					"d3dx11"
+		}
+		return true
+end