Set POSITION_INDEPENDENT_CODE property on SDL2 for CMake 3.0

CMakeLists.txt

@@ -2939,6 +2939,7 @@ if(SDL_SHARED)
   add_library(SDL2 SHARED ${SOURCE_FILES} ${VERSION_SOURCES})
   # alias target for in-tree builds
   add_library(SDL2::SDL2 ALIAS SDL2)
+  set_target_properties(SDL2 PROPERTIES POSITION_INDEPENDENT_CODE TRUE)
   if(APPLE)
     set_target_properties(SDL2 PROPERTIES
       MACOSX_RPATH 1