[libc++][C++20 modules] Tests no unicode build.

[Mordante]

Summary

Depends on D158347

libcxx/cmake/caches/Generic-no-unicode.cmake

+set(LIBCXX_ENABLE_STD_MODULES ON CACHE BOOL "") # TODO MODULES Remove when enabled automatically.
 set(LIBCXX_ENABLE_UNICODE OFF CACHE BOOL "")

libcxx/docs/Modules.rst

  * Using the ``std`` module in external projects
  * The following "parts disabled" configuration options are supported
 
    * ``LIBCXX_ENABLE_LOCALIZATION``
    * ``LIBCXX_ENABLE_WIDE_CHARACTERS``
    * ``LIBCXX_ENABLE_THREADS``
    * ``LIBCXX_ENABLE_FILESYSTEM``
    * ``LIBCXX_ENABLE_RANDOM_DEVICE``
+   * ``LIBCXX_ENABLE_UNICODE``
 
 Some of the current limitations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
  * There is no official build system support, libc++ has experimental CMake support
  * Requires CMake 3.26 for C++23 support
  * Requires CMake 3.27 for C++26 support
  * Requires Ninja 1.11

libcxx/modules/CMakeLists.txt.in

macro(compile_define_if_not condition def)
   endif()
 endmacro()
 macro(compile_define_if condition def)
   if (${condition})
     target_compile_definitions(std PRIVATE ${def})
   endif()
 endmacro()
 
-if(NOT @LIBCXX_ENABLE_UNICODE@)
-  message(FATAL_ERROR "Modules without Unicode support is not yet implemented.")
-endif()
 if(NOT @LIBCXX_ENABLE_EXCEPTIONS@ OR NOT @LIBCXXABI_ENABLE_EXCEPTIONS@)
   message(FATAL_ERROR "Modules without exception support is not yet implemented.")
 endif()
 
 add_library(std)
 target_sources(std
   PUBLIC FILE_SET cxx_modules TYPE CXX_MODULES FILES
     std.cppm

libcxx/modules/std/print.inc

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 export namespace std {
   // [print.fun], print functions
   using std::print;
   using std::println;
 
   using std::vprint_nonunicode;
+#ifndef _LIBCPP_HAS_NO_UNICODE
   using std::vprint_unicode;
+#endif // _LIBCPP_HAS_NO_UNICODE
 } // namespace std

libcxx/utils/ci/buildkite-pipeline.yml

- label: "No locale"
       timeout_in_minutes: 120
 
     - label: "No Unicode"
       command: "libcxx/utils/ci/run-buildbot generic-no-unicode"
       artifact_paths:
         - "**/test-results.xml"
         - "**/*.abilist"
       env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
+          # Note: Modules require and absolute path for clang-scan-deps
+          # https://github.com/llvm/llvm-project/issues/61006
+          CC: "/usr/lib/llvm-${LLVM_HEAD_VERSION}/bin/clang"
+          CXX: "/usr/lib/llvm-${LLVM_HEAD_VERSION}/bin/clang++"
+          CMAKE: "/opt/bin/cmake"
           ENABLE_CLANG_TIDY: "On"
       agents:
         queue: "libcxx-builders"
         os: "linux"
       retry:
         automatic:
           - exit_status: -1  # Agent was lost
             limit: 2