[Clang-CL] source_location is not available in clang-cl tool with /std:c++20

[danakj]

A clang tool on Windows uses clang-cl, which uses the MSVC library, and the <source_location> header contains this:

#pragma once
#ifndef _SOURCE_LOCATION_
#define _SOURCE_LOCATION_
#include <yvals_core.h>
#if _STL_COMPILER_PREPROCESSOR
#ifndef __cpp_consteval
_EMIT_STL_WARNING(STL4038, "The contents of <source_location> are available only with C++20 consteval support.");
#else // ^^^ !defined(__cpp_consteval) / defined(__cpp_consteval) vvv

If I pass /D__cpp_consteval then source_location is there. As consteval is supported in Clang with C++20, should clang-cl tooling automatically set this define?

This is possibly related to #59689 where _CRT_USE_BUILTIN_OFFSETOF is not defined in a clang-cl tool.

[alvinhochun]

Related to #57094

[llvmbot]

@llvm/issue-subscribers-c-20

[AaronBallman]

Duplicate of #57094