Properly set BACKGROUND_GC variant for the DAC (#119123)

* This setting was previously inverted from the intended behavior

Author: max-charlamb

src/coreclr/gc/gc.cpp

@@ -53680,9 +53680,9 @@ void PopulateDacVars(GcDacVars *gcDacVars)
         gcDacVars->global_free_huge_regions = reinterpret_cast<dac_region_free_list**>(&gc_heap::global_free_huge_regions);
     }
 #endif //USE_REGIONS
-#ifndef BACKGROUND_GC
+#ifdef BACKGROUND_GC
     g_build_variant |= build_variant_background_gc;
-#endif //!BACKGROUND_GC
+#endif //BACKGROUND_GC
 #ifdef DYNAMIC_HEAP_COUNT
     g_build_variant |= build_variant_dynamic_heap_count;
 #endif //DYNAMIC_HEAP_COUNT