opengl: Declare fragment outputs even if they are not used

Fixes Ori and the Blind Forest's menu on GLASM. For some reason
(probably high level optimizations) it is not sanitized on SPIR-V for
OpenGL. Vulkan is unaffected by this change.

src/shader_recompiler/backend/spirv/emit_context.cpp

@@ -1320,7 +1320,7 @@ void EmitContext::DefineOutputs(const IR::Program& program) {
         break;
     case Stage::Fragment:
         for (u32 index = 0; index < 8; ++index) {
-            if (!info.stores_frag_color[index]) {
+            if (!info.stores_frag_color[index] && !profile.need_declared_frag_colors) {
                 continue;
             }
             frag_color[index] = DefineOutput(*this, F32[4], std::nullopt);