support SPV_NV_viewport_array2 and SPV_NV_stereo_view_rendering

Test/spv.viewportArray2.vert

@@ -0,0 +1,10 @@
+#version 450
+#extension GL_ARB_shader_viewport_layer_array : require
+#extension GL_NV_viewport_array2 : require
+
+layout (viewport_relative) out highp int gl_Layer;
+void main()
+{
+    gl_ViewportMask[0]            = 1;
+    gl_ViewportIndex              = 2;
+}