fix compilation on MINGW

examples/opengl3_example/Makefile

@@ -39,7 +39,7 @@ ifeq ($(UNAME_S), Darwin) #APPLE
 	CFLAGS = $(CXXFLAGS)
 endif
 
-ifeq ($(UNAME_S), MINGW64_NT-6.3)
+ifeq ($(findstring MINGW,$(UNAME_S)),MINGW)
    ECHO_MESSAGE = "Windows"
    LIBS = -lglfw3 -lgdi32 -lopengl32 -limm32