Workaround for gcc 4.8.2: Suppress mkl-dnn warning manually since pragma GCC…

Workaround for gcc 4.8.2: Suppress mkl-dnn warning manually since pragma GCC diagnostic ignored is not working on gcc 4.8.2 (#2812)

cmake/external_mkldnn.cmake

@@ -105,10 +105,13 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
         if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 8.0 OR CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 8.0)
             set(MKLDNN_FLAG "-Wno-stringop-truncation -Wno-stringop-overflow")
         endif()
-    elseif(NGRAPH_MANYLINUX_ENABLE) #pragma GCC diagnostic ignored does not work on GCC used for manylinux1
+    elseif(LINUX)
+        if(CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 4.8.2)
+            #pragma GCC diagnostic ignored does not work on GCC used for manylinux1
             set(MKLDNN_FLAG "-Wno-error=strict-overflow -Wno-error=unused-result -Wno-error=array-bounds")
             set(MKLDNN_FLAG "${MKLDNN_FLAG} -Wno-unused-result -Wno-unused-value")
         endif()
+    endif()
 endif()
 
 ExternalProject_Add(