[llvm-bugs] [Bug 42027] New: [Win] LNK2005: bool const std::_Is_integral<bool> already defined

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42027

            Bug ID: 42027
           Summary: [Win] LNK2005: bool const std::_Is_integral<bool>
                    already defined
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mikhail.strelnikov at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

Self-hosting on Windows
(https://github.com/llvm/llvm-project/blob/master/llvm/utils/release/build_llvm_package.bat)
is broken by this commit:

https://github.com/llvm-mirror/clang/commit/4241f674da3531d69abc759d727fb0ae7b31535e

Another way to reproduce the bug:

// h.hpp
#pragma once

template<typename T>
constexpr bool v = false;

template <>
constexpr bool v<bool> = true;

// unit1.cpp
#include "h.hpp"

// unit2.cpp
#include "h.hpp"

int main()
{
        return v<bool>;
}

# clang++ -std=c++14 unit1.cpp unit2.cpp
error LNK2005: "bool const v<bool>" (??$v at _N@@3_NB) already defined

I've no idea if it is OK code for C++14, but this is what MS STL does in its
<xtr1common> header.

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