Core: Don't link to imgui for libretro core

src/core/gpu_hw.cpp

@@ -3,13 +3,15 @@
 #include "common/log.h"
 #include "common/state_wrapper.h"
 #include "cpu_core.h"
-#include "imgui.h"
 #include "pgxp.h"
 #include "settings.h"
 #include "system.h"
 #include <cmath>
 #include <sstream>
 #include <tuple>
+#ifdef WITH_IMGUI
+#include "imgui.h"
+#endif
 Log_SetChannel(GPU_HW);
 
 template<typename T>
@@ -1000,6 +1002,7 @@ void GPU_HW::DrawRendererStats(bool is_idle_frame)
     m_renderer_stats = {};
   }
 
+#ifdef WITH_IMGUI
   if (ImGui::CollapsingHeader("Renderer Statistics", ImGuiTreeNodeFlags_DefaultOpen))
   {
     static const ImVec4 active_color{1.0f, 1.0f, 1.0f, 1.0f};
@@ -1068,4 +1071,5 @@ void GPU_HW::DrawRendererStats(bool is_idle_frame)
 
     ImGui::Columns(1);
   }
+#endif
 }