GLSL: Make gl_Layer and gl_ViewportIndex always be outside blocks.

There was some ambiguity/contradiction in this behavior, and
Khronos decided glslang should always have these outside blocks,
rather than have stage/vendor/target variations.

Test/spv.stereoViewRendering.tesc

@@ -8,9 +8,10 @@ layout(vertices = 4) out;
 out gl_PerVertex {
     int gl_SecondaryViewportMaskNV[2];
     vec4 gl_SecondaryPositionNV;
-    layout (viewport_relative, secondary_view_offset = 1) out highp int gl_Layer;
 } gl_out[4];
 
+layout (viewport_relative, secondary_view_offset = 1) out highp int gl_Layer;
+
 void main()
 {
     gl_out[gl_InvocationID].gl_SecondaryViewportMaskNV[0]            = 1;