[CMake] Copy the generated __config header into build directory

[phosek]

Summary

When the generated config file is being used, it is currently only
copied during installation process. However, that means that the file
that gets copied into LLVM build directory is the vanilla config file,
and any parts of the build that depend on the just built toolchain like
sanitizers will get that instead of the generated version. To avoid this
issue, we need to copy the generated header into the LLVM build
directory as well.

[phosek]

Ping? Can we land this as a temporary solution until the config generator logic is rewritten? This is currently breaking the libFuzzer build for us.

[phosek]

Ping again?

[compnerd]

libcxx/include/CMakeLists.txt

19

Where is generated_config_deps used?

[phosek]

libcxx/include/CMakeLists.txt

19

Line 69

libcxx/include/CMakeLists.txt

 if (NOT LIBCXX_INSTALL_SUPPORT_HEADERS)
   set(LIBCXX_SUPPORT_HEADER_PATTERN PATTERN "support" EXCLUDE)
 endif()
 
+if (LIBCXX_NEEDS_SITE_CONFIG)
+  # Generate a custom __config header. The new header is created
+  # by prepending __config_site to the current __config header.
+  add_custom_command(OUTPUT ${LIBCXX_BINARY_DIR}/__generated_config
+    COMMAND ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/cat_files.py
+      ${LIBCXX_BINARY_DIR}/__config_site
+      ${LIBCXX_SOURCE_DIR}/include/__config
+      -o ${LIBCXX_BINARY_DIR}/__generated_config
+    DEPENDS ${LIBCXX_SOURCE_DIR}/include/__config
+            ${LIBCXX_BINARY_DIR}/__config_site
+  )
+  # Add a target that executes the generation commands.
+  add_custom_target(generate_config_header ALL
+    DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
+  set(generated_config_deps generate_config_header)
+endif()
+
 set(LIBCXX_HEADER_PATTERN
   PATTERN "*"
   PATTERN "CMakeLists.txt" EXCLUDE
   PATTERN ".svn" EXCLUDE
   PATTERN "__config_site.in" EXCLUDE
   ${LIBCXX_SUPPORT_HEADER_PATTERN}
   )
 
 if(NOT LIBCXX_USING_INSTALLED_LLVM AND LLVM_BINARY_DIR)
   file(COPY .
     DESTINATION "${LLVM_BINARY_DIR}/include/c++/v1"
     FILES_MATCHING
     ${LIBCXX_HEADER_PATTERN}
     )
+
+  if (LIBCXX_NEEDS_SITE_CONFIG)
+    # Copy the generated header as __config into build directory.
+    add_custom_command(
+        TARGET generate_config_header POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy
+                ${LIBCXX_BINARY_DIR}/__generated_config
+                ${LLVM_BINARY_DIR}/include/c++/v1/__config)
+  endif()
 endif()
 
 if (LIBCXX_INSTALL_HEADERS)
   install(DIRECTORY .
     DESTINATION ${LIBCXX_INSTALL_PREFIX}include/c++/v1
     COMPONENT cxx-headers
     FILES_MATCHING
     ${LIBCXX_HEADER_PATTERN}
     PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
   )
 
   if (LIBCXX_NEEDS_SITE_CONFIG)
-    # Generate and install a custom __config header. The new header is created
-    # by  prepending __config_site to the current __config header.
-    add_custom_command(OUTPUT ${LIBCXX_BINARY_DIR}/__generated_config
-      COMMAND ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/cat_files.py
-        ${LIBCXX_BINARY_DIR}/__config_site
-        ${LIBCXX_SOURCE_DIR}/include/__config
-        -o ${LIBCXX_BINARY_DIR}/__generated_config
-      DEPENDS ${LIBCXX_SOURCE_DIR}/include/__config
-              ${LIBCXX_BINARY_DIR}/__config_site
-    )
-    # Add a target that executes the generation commands.
-    add_custom_target(generate_config_header ALL
-      DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
-    set(generated_config_deps generate_config_header)
     # Install the generated header as __config.
     install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
       DESTINATION ${LIBCXX_INSTALL_PREFIX}include/c++/v1
       PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
       RENAME __config
       COMPONENT cxx-headers)
   endif()