used native LTO support from cmake 3.9.6 (#2625)

* used native LTO support from cmake 3.9.6

* Removed compilation flags push / pop

* Fixes

* Fixes for VPU unit tests

* Temp WA for old gcc

docs/template_plugin/CMakeLists.txt

@@ -14,12 +14,12 @@ find_package(InferenceEngineDeveloperPackage REQUIRED)
 add_subdirectory(src)
 
 if(ENABLE_TESTS)
-	include(CTest)
-	enable_testing()
+    include(CTest)
+    enable_testing()
 
-	if(ENABLE_FUNCTIONAL_TESTS)
-	    add_subdirectory(tests/functional)
-	endif()
+    if(ENABLE_FUNCTIONAL_TESTS)
+        add_subdirectory(tests/functional)
+    endif()
 endif()
 # [cmake:main]
 

docs/template_plugin/src/CMakeLists.txt

@@ -5,10 +5,6 @@
 # [cmake:plugin]
 set(TARGET_NAME "templatePlugin")
 
-if(ENABLE_LTO)
-    ie_enable_lto()
-endif()
-
 file(GLOB SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp)
 file(GLOB_RECURSE HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/*.hpp)
 
@@ -20,9 +16,7 @@ ie_add_plugin(NAME ${TARGET_NAME}
               VERSION_DEFINES_FOR template_plugin.cpp)
 
 target_include_directories(${TARGET_NAME} PRIVATE
-    "${CMAKE_CURRENT_SOURCE_DIR}")
-
-target_include_directories(${TARGET_NAME} PRIVATE
+    "${CMAKE_CURRENT_SOURCE_DIR}"
     "${IE_MAIN_TEMPLATE_PLUGIN_SOURCE_DIR}/include")
 
 # link common Inference Engine libraries
@@ -36,6 +30,8 @@ target_link_libraries(${TARGET_NAME} PRIVATE
     IE::ngraph_backend
     IE::interpreter_backend)
 
+set_target_properties(${TARGET_NAME} PROPERTIES INTERPROCEDURAL_OPTIMIZATION ${ENABLE_LTO})
+
 # ATTENTION: uncomment to register a plugin in the plugins.xml file
 # ie_register_plugins(MAIN_TARGET ${TARGET_NAME}
 #                     POSSIBLE_PLUGINS ${TARGET_NAME})

docs/template_plugin/tests/functional/CMakeLists.txt

@@ -3,10 +3,6 @@
 # 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)