use external miniupnpc if available

external/CMakeLists.txt

@@ -1,8 +1,18 @@
-if(NOT FREEBSD)
+if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+	include(FindMiniupnpc)
+endif()
+
+if(MINIUPNP_FOUND AND MINIUPNPC_VERSION_1_7_OR_HIGHER)
+  message(STATUS "Using shared miniupnpc")
+  include_directories(${MINIUPNP_INCLUDE_DIR})
+  set(UPNP_LIBRARIES "miniupnpc")
+else()
+  message(STATUS "Using static miniupnpc from external")
+  add_subdirectory(miniupnpc)
+
   set(UPNPC_BUILD_STATIC ON CACHE BOOL "Build static library")
   set(UPNPC_BUILD_SHARED OFF CACHE BOOL "Build shared library")
   set(UPNPC_BUILD_TESTS OFF CACHE BOOL "Build test executables")
-  add_subdirectory(miniupnpc)
 
   set_property(TARGET upnpc-static PROPERTY FOLDER "external")
   if(MSVC)
@@ -10,4 +20,6 @@ if(NOT FREEBSD)
   elseif(NOT MSVC)
     set_property(TARGET upnpc-static APPEND_STRING PROPERTY COMPILE_FLAGS " -Wno-undef -Wno-unused-result -Wno-unused-value")
   endif()
-endif()
+
+  set(UPNP_LIBRARIES "upnpc-static")
+endif()