glsl: skip gl_ViewportIndex write if device does not support it

src/shader_recompiler/profile.h

@@ -85,6 +85,7 @@ struct Profile {
     bool support_derivative_control{};
     bool support_gl_nv_gpu_shader_5{};
     bool support_gl_amd_gpu_shader_half_float{};
+    bool support_gl_vertex_viewport_layer{};
 
     bool warp_size_potentially_larger_than_guest{};