stb_wingraph.h: missing lib pragmas for completeness

tests/oversample/stb_wingraph.h

@@ -25,6 +25,8 @@
    #pragma comment(lib, "opengl32.lib")
    #pragma comment(lib, "glu32.lib")
    #pragma comment(lib, "winmm.lib")
+   #pragma comment(lib, "gdi32.lib")
+   #pragma comment(lib, "user32.lib")
 #endif
 
 #ifdef __cplusplus