Provide empty {Gpu,Vk}CtxScope classes if tracy is disabled.

This may be needed if some wrapping is done, abstracting the OpenGL and
Vulkan tracing.

TracyOpenGL.hpp

@@ -17,6 +17,11 @@
 #define TracyGpuZoneS(x,y)
 #define TracyGpuZoneCS(x,y,z)
 
+namespace tracy
+{
+class GpuCtxScope {};
+}
+
 #else
 
 #include <atomic>

TracyVulkan.hpp

@@ -16,6 +16,11 @@
 #define TracyVkZoneS(c,x,y,z)
 #define TracyVkZoneCS(c,x,y,z,w)
 
+namespace tracy
+{
+class VkCtxScope {};
+}
+
 using TracyVkCtx = void*;
 
 #else