Fix ATen/core header installation. (pytorch#10463)

Summary:
Fixes pytorch#10353 and fixes pytorch#10397.

Signed-off-by: Edward Z. Yang <[email protected]>
Pull Request resolved: pytorch#10463

Differential Revision: D9296491

Pulled By: ezyang

fbshipit-source-id: f825c2a21a113e44a6f5c1c5ec17814d9deac366

Author: ezyang

caffe2/CMakeLists.txt

@@ -59,8 +59,7 @@ else()
   list(APPEND Caffe2_CPU_SRCS ${ATen_CORE_SRCS})
   list(APPEND Caffe2_CPU_INCLUDE ${ATen_CORE_INCLUDE})
   list(APPEND Caffe2_CPU_TEST_SRCS ${ATen_CORE_TEST_SRCS})
-  # TODO: We should probably install the headers, but I don't know
-  # how to do that.
+  # See cmake/Codegen.cmake for header installation
 endif()
 
 # ---[ Torch build

cmake/Codegen.cmake

@@ -22,7 +22,7 @@ install(DIRECTORY ${CMAKE_CURRENT_LIST_DIR}/../caffe2
         FILES_MATCHING PATTERN "*.h")
 if (NOT BUILD_ATEN)
   install(DIRECTORY ${CMAKE_CURRENT_LIST_DIR}/../aten/src/ATen/core
-          DESTINATION include/ATen/core
+          DESTINATION include/ATen
           FILES_MATCHING PATTERN "*.h")
 endif()
 install(FILES ${CMAKE_BINARY_DIR}/caffe2/core/macros.h