glsl: Obey need_declared_frag_colors to declare and initialize all frag_color

Fixes Ori and the blind forest title screen

src/shader_recompiler/backend/glsl/emit_context.cpp

@@ -340,7 +340,7 @@ EmitContext::EmitContext(IR::Program& program, Bindings& bindings, const Profile
         header += fmt::format("layout(location={})patch {} vec4 patch{};", index, qualifier, index);
     }
     for (size_t index = 0; index < info.stores_frag_color.size(); ++index) {
-        if (!info.stores_frag_color[index]) {
+        if (!info.stores_frag_color[index] && !profile.need_declared_frag_colors) {
             continue;
         }
         header += fmt::format("layout(location={})out vec4 frag_color{};", index, index);

src/shader_recompiler/backend/glsl/emit_glsl_special.cpp

@@ -8,6 +8,7 @@
 #include "shader_recompiler/backend/glsl/emit_glsl_instructions.h"
 #include "shader_recompiler/frontend/ir/program.h"
 #include "shader_recompiler/frontend/ir/value.h"
+#include "shader_recompiler/profile.h"
 
 namespace Shader::Backend::GLSL {
 namespace {
@@ -58,6 +59,14 @@ void EmitPrologue(EmitContext& ctx) {
     if (ctx.StageInitializesVaryings()) {
         InitializeVaryings(ctx);
     }
+    if (ctx.stage == Stage::Fragment && ctx.profile.need_declared_frag_colors) {
+        for (size_t index = 0; index < ctx.info.stores_frag_color.size(); ++index) {
+            if (ctx.info.stores_frag_color[index]) {
+                continue;
+            }
+            ctx.Add("frag_color{}=vec4(0,0,0,1);", index);
+        }
+    }
 }
 
 void EmitEpilogue(EmitContext&) {}