Fixed LTO for gcc-9 (ubuntu 20.04) (#2616)

* Fixed LTO for gcc-9 (ubuntu 20.04)

* Fixed ODR rules violation for MKLDNN deprecated functional tests

* Fixed tests build for templatePlugin

docs/template_plugin/tests/functional/CMakeLists.txt

@@ -3,6 +3,10 @@
 # SPDX-License-Identifier: Apache-2.0
 #
 
+if(ENABLE_LTO AND CMAKE_COMPILER_IS_GNUCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 9.0)
+    ie_enable_lto()
+endif()
+
 # [cmake:functional_tests]
 set(TARGET_NAME templateFuncTests)