Fix colliding of miniupnpc.lib files

Fix miniupnp/miniupnp#270

Both libminiupnpc-static and libminiupnpc-shared targets
were generated miniupnpc.lib files.
Now libminiupnpc-static generates libminiupnpc.lib whereas
libminiupnpc-shared generates miniupnpc.lib and miniupnpc.dll

CMakeLists.txt

@@ -99,7 +99,11 @@ endif ()
 
 if (UPNPC_BUILD_STATIC)
   add_library (libminiupnpc-static STATIC ${MINIUPNPC_SOURCES})
-  set_target_properties (libminiupnpc-static PROPERTIES OUTPUT_NAME "miniupnpc")
+  if (WIN32)
+    set_target_properties (libminiupnpc-static PROPERTIES OUTPUT_NAME "libminiupnpc")
+  else()
+    set_target_properties (libminiupnpc-static PROPERTIES OUTPUT_NAME "miniupnpc")
+  endif()
   target_link_libraries (libminiupnpc-static PRIVATE miniupnpc-private)
   target_include_directories(libminiupnpc-static INTERFACE ../${CMAKE_CURRENT_SOURCE_DIR})
   target_compile_definitions(libminiupnpc-static PUBLIC MINIUPNP_STATICLIB)