Issue with xxhash_cpp

a.cpp

#include "xxhash.hpp"
#include <iostream>

extern void process();

int main(int, char **)
{
    process();
    std::cout << "xxhash<32>(1) => " << xxh::xxhash<32>(std::array<uint32_t, 1>{1}) << std::endl;
}

b.cpp

#include "xxhash.hpp"
#include <iostream>

void process()
{
    std::cout << "xxhash<32>(1) => " << xxh::xxhash<32>(std::array<uint32_t, 1>{1}) << std::endl;
}

Build the two files by putting them and xxhash.hpp from this commit in a directory & using the command

cl.exe a.cpp b.cpp -EHsc -std:c++17 

You should see the following output:

Microsoft (R) C/C++ Optimizing Compiler Version 19.16.27041 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

a.cpp
b.cpp
Generating Code...
Microsoft (R) Incremental Linker Version 14.16.27041.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:a.exe
a.obj
b.obj
b.obj : error LNK2005: "void __cdecl xxh::intrin::prefetch(void const *)" (?prefetch@intrin@xxh@@YAXPEBX@Z) already defined in a.obj
a.exe : fatal error LNK1169: one or more multiply defined symbols found