private function to static initialize all the backend for static library builds (#3379)

* - private function to static initlize all the backend for static library builds

* - export backend function on windows

* -fix_typo

src/ngraph/runtime/backend_manager.cpp

@@ -53,6 +53,7 @@ void runtime::BackendManager::register_backend(const string& name, BackendConstr
 
 vector<string> runtime::BackendManager::get_registered_backends()
 {
+    initialize_backends();
     vector<string> rc;
     for (const auto& p : get_registry())
     {
@@ -67,8 +68,7 @@ vector<string> runtime::BackendManager::get_registered_backends()
     }
     return rc;
 }
-
-shared_ptr<runtime::Backend> runtime::BackendManager::create_backend(const std::string& config)
+void runtime::BackendManager::initialize_backends()
 {
 #ifdef NGRAPH_INTERPRETER_STATIC_LIB_ENABLE
     runtime::interpreter::static_initialize();
@@ -77,7 +77,11 @@ shared_ptr<runtime::Backend> runtime::BackendManager::create_backend(const std::
 #ifdef NGRAPH_CPU_STATIC_LIB_ENABLE
     runtime::cpu::static_initialize();
 #endif
+}
 
+shared_ptr<runtime::Backend> runtime::BackendManager::create_backend(const std::string& config)
+{
+    initialize_backends();
     shared_ptr<runtime::Backend> backend;
     string type = config;
 

src/ngraph/runtime/backend_manager.hpp

@@ -64,6 +64,7 @@ public:
     static std::vector<std::string> get_registered_backends();
 
 private:
+    static void initialize_backends();
     static std::shared_ptr<runtime::Backend> create_backend(const std::string& type);
     static std::unordered_map<std::string, BackendConstructor*>& get_registry();