CMake: Set default visibility to hidden and dllexport on windows

CMakeLists.txt

@@ -61,6 +61,16 @@ if (ENABLE_SANITIZERS)
         )
 endif()
 
+option(ENABLE_PUBLIC_SYMBOLS "Export library symbols." On)
+if (ENABLE_PUBLIC_SYMBOLS)
+    list(APPEND custom_compiler_flags -fvisibility=hidden)
+    add_definitions(-DCJSON_EXPORT_SYMBOLS -DCJSON_API_VISIBILITY)
+endif()
+option(ENABLE_HIDDEN_SYMBOLS "Hide library symbols." Off)
+if (ENABLE_HIDDEN_SYMBOLS)
+    add_definitions(-DCJSON_HIDE_SYMBOLS -UCJSON_API_VISIBILITY)
+endif()
+
 # apply custom compiler flags
 foreach(compiler_flag ${custom_compiler_flags})
     #remove problematic characters