Patch mkldnn for build on gcc 4.8.2 (#10616)

* test_patch_mkldnn

* use patch file

* follow comments

* fix patch

Author: typhoonzero

cmake/external/mkldnn.cmake

@@ -56,6 +56,8 @@ ExternalProject_Add(
     GIT_TAG             "v0.14"
     PREFIX              ${MKLDNN_SOURCES_DIR}
     UPDATE_COMMAND      ""
+    # Patch MKLDNN to compile with gcc 4.8, the related issue is in intel/mkl-dnn#237.
+    PATCH_COMMAND       ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_SOURCE_DIR}/patches/mkldnn.hpp ${MKLDNN_SOURCES_DIR}/src/extern_mkldnn/include/mkldnn.hpp
     CMAKE_ARGS          -DCMAKE_INSTALL_PREFIX=${MKLDNN_INSTALL_DIR}
     CMAKE_ARGS          -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} 
     CMAKE_ARGS          -DMKLROOT=${MKLML_ROOT}