emit_glasm: Enable ARB_draw_buffers when needed

src/shader_recompiler/backend/glasm/emit_context.cpp

@@ -71,7 +71,7 @@ EmitContext::EmitContext(IR::Program& program) {
         if (index == 0) {
             Add("OUTPUT frag_color0=result.color;");
         } else {
-            Add("OUTPUT frag_color{}[]=result.color[{}];", index, index);
+            Add("OUTPUT frag_color{}=result.color[{}];", index, index);
         }
     }
     for (size_t index = 0; index < program.info.stores_generics.size(); ++index) {

src/shader_recompiler/backend/glasm/emit_glasm.cpp

@@ -283,6 +283,10 @@ void SetupOptions(std::string& header, Info info) {
     if (info.uses_subgroup_shuffles) {
         header += "OPTION NV_shader_thread_shuffle;";
     }
+    const auto non_zero_frag_colors{info.stores_frag_color | std::views::drop(1)};
+    if (std::ranges::find(non_zero_frag_colors, true) != non_zero_frag_colors.end()) {
+        header += "OPTION ARB_draw_buffers;";
+    }
 }
 
 std::string_view StageHeader(Stage stage) {