[libcxx] Fix include directory order (#65859)

It's important that the arch directory be included first so that
its header files which interpose on the default include dir
be included instead of the default ones. The clang driver [1] does
this when not building with -nostdinc, the libcxx build should
do the same.

We found this after https://reviews.llvm.org/D154282 when cross
compiling from non Linux to Linux. If the host machine was not
Linux, _LIBCPP_HAS_NO_TIME_ZONE_DATABASE would be defined in
the default include dir __config_site, while it was undefined
in the arch specific one causing build failures.

Author: abrachet

libcxx/include/CMakeLists.txt

@@ -1029,8 +1029,10 @@ add_custom_target(generate-cxx-headers ALL DEPENDS ${_all_includes})
 add_library(cxx-headers INTERFACE)
 target_link_libraries(cxx-headers INTERFACE libcxx-abi-headers)
 add_dependencies(cxx-headers generate-cxx-headers)
-target_include_directories(cxx-headers INTERFACE ${LIBCXX_GENERATED_INCLUDE_DIR}
-                                                 ${LIBCXX_GENERATED_INCLUDE_TARGET_DIR})
+# It's important that the arch directory be included first so that its header files
+# which interpose on the default include dir be included instead of the default ones.
+target_include_directories(cxx-headers INTERFACE ${LIBCXX_GENERATED_INCLUDE_TARGET_DIR}
+                                                 ${LIBCXX_GENERATED_INCLUDE_DIR})
 
 if (LIBCXX_INSTALL_HEADERS)
   foreach(file ${files})

libcxx/modules/CMakeLists.txt

@@ -128,8 +128,10 @@ if ("${LIBCXX_GENERATED_INCLUDE_DIR}" STREQUAL "${LIBCXX_GENERATED_INCLUDE_TARGE
   # This typically happens when the target is not installed.
   set(LIBCXX_CONFIGURED_INCLUDE_DIRS "${LIBCXX_GENERATED_INCLUDE_DIR}")
 else()
+  # It's important that the arch directory be included first so that its header files
+  # which interpose on the default include dir be included instead of the default ones.
   set(LIBCXX_CONFIGURED_INCLUDE_DIRS
-    "${LIBCXX_GENERATED_INCLUDE_DIR};${LIBCXX_GENERATED_INCLUDE_TARGET_DIR}"
+    "${LIBCXX_GENERATED_INCLUDE_TARGET_DIR};${LIBCXX_GENERATED_INCLUDE_DIR}"
   )
 endif()
 configure_file(