diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -874,22 +874,15 @@
 endif()
 
 set(site_config_path "${LIBCXX_BINARY_DIR}/__config_site")
-if (LIBCXX_NEEDS_SITE_CONFIG)
-  configure_file("include/__config_site.in"
-                 "${site_config_path}"
-                 @ONLY)
-elseif(EXISTS "${site_config_path}")
-  message(STATUS "Removing stale site configuration ${site_config_path}")
-  file(REMOVE "${site_config_path}")
-endif()
+configure_file("include/__config_site.in"
+               "${site_config_path}"
+               @ONLY)
 
 function(cxx_add_config_site target)
-  if (LIBCXX_NEEDS_SITE_CONFIG)
-    if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
-      target_compile_options(${target} PUBLIC /FI "${site_config_path}")
-    else()
-      target_compile_options(${target} PUBLIC -include "${site_config_path}")
-    endif()
+  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
+    target_compile_options(${target} PUBLIC /FI "${site_config_path}")
+  else()
+    target_compile_options(${target} PUBLIC -include "${site_config_path}")
   endif()
 endfunction()
 
diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt
--- a/libcxx/benchmarks/CMakeLists.txt
+++ b/libcxx/benchmarks/CMakeLists.txt
@@ -18,9 +18,7 @@
           -L${LIBCXX_CXX_ABI_LIBRARY_PATH}
           -Wl,-rpath,${LIBCXX_CXX_ABI_LIBRARY_PATH})
 endif()
-if (LIBCXX_NEEDS_SITE_CONFIG)
-  list(APPEND BENCHMARK_LIBCXX_COMPILE_FLAGS -include "${LIBCXX_BINARY_DIR}/__config_site")
-endif()
+list(APPEND BENCHMARK_LIBCXX_COMPILE_FLAGS -include "${LIBCXX_BINARY_DIR}/__config_site")
 split_list(BENCHMARK_LIBCXX_COMPILE_FLAGS)
 
 ExternalProject_Add(google-benchmark-libcxx
diff --git a/libcxx/cmake/Modules/HandleLibcxxFlags.cmake b/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
--- a/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
+++ b/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
@@ -88,20 +88,17 @@
 macro(config_define_if condition def)
   if (${condition})
     set(${def} ON)
-    set(LIBCXX_NEEDS_SITE_CONFIG ON)
   endif()
 endmacro()
 
 macro(config_define_if_not condition def)
   if (NOT ${condition})
     set(${def} ON)
-    set(LIBCXX_NEEDS_SITE_CONFIG ON)
   endif()
 endmacro()
 
 macro(config_define value def)
   set(${def} ${value})
-  set(LIBCXX_NEEDS_SITE_CONFIG ON)
 endmacro()
 
 # Add a list of flags to all of 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS',
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -184,27 +184,20 @@
     )
 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 ${Python3_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(cxx-generated-config ALL
-    DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
-  set(generated_config_deps cxx-generated-config)
-else()
-  set(files
-    ${files}
-    __config
-    )
-endif()
+# 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 ${Python3_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(cxx-generated-config ALL
+  DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
+set(generated_config_deps cxx-generated-config)
 
 # In some build configurations (like bootstrapping clang), we need to be able to
 # install the libcxx headers before the CMake configuration for libcxx runs. Making
@@ -228,16 +221,14 @@
     list(APPEND out_files ${dst})
   endforeach()
 
-  if (LIBCXX_NEEDS_SITE_CONFIG)
-    # Copy the generated header as __config into build directory.
-    set(src ${LIBCXX_BINARY_DIR}/__generated_config)
-    set(dst ${output_dir}/__config)
-    add_custom_command(OUTPUT ${dst}
-        DEPENDS ${src} ${generated_config_deps}
-        COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
-        COMMENT "Copying CXX __config")
-    list(APPEND out_files ${dst})
-  endif()
+  # Copy the generated header as __config into build directory.
+  set(src ${LIBCXX_BINARY_DIR}/__generated_config)
+  set(dst ${output_dir}/__config)
+  add_custom_command(OUTPUT ${dst}
+      DEPENDS ${src} ${generated_config_deps}
+      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+      COMMENT "Copying CXX __config")
+  list(APPEND out_files ${dst})
 
   add_custom_target(${CXX_HEADER_TARGET} ALL DEPENDS ${out_files} ${LIBCXX_CXX_ABI_HEADER_TARGET})
 else()
@@ -255,14 +246,12 @@
     )
   endforeach()
 
-  if (LIBCXX_NEEDS_SITE_CONFIG)
-    # Install the generated header as __config.
-    install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
-      DESTINATION ${LIBCXX_INSTALL_HEADER_PREFIX}include/c++/v1
-      PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
-      RENAME __config
-      COMPONENT ${CXX_HEADER_TARGET})
-  endif()
+  # Install the generated header as __config.
+  install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
+    DESTINATION ${LIBCXX_INSTALL_HEADER_PREFIX}include/c++/v1
+    PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+    RENAME __config
+    COMPONENT ${CXX_HEADER_TARGET})
 
   if (NOT CMAKE_CONFIGURATION_TYPES)
     add_custom_target(install-${CXX_HEADER_TARGET}