__emulu() is not available on arm

[liubing]

Version of Boost

boost 1.83beta

Steps necessary to reproduce the problem

Compile the library on arm64 / windows platform.

All relevant compiler information

Error message:

D:\Projects\pts\pts\include\boost\json\detail\charconv\detail\emulated128.hpp(62): error C3861: '__emulu': identifier not found

It can be fixed changing

static inline std::uint64_t umul64(std::uint32_t x, std::uint32_t y) noexcept
{
#if defined(BOOST_JSON_HAS_MSVC_32BIT_INTRINSICS)
    return __emulu(x, y);
#else
    return x * static_cast<std::uint64_t>(y);
#endif
}

to

static inline std::uint64_t umul64(std::uint32_t x, std::uint32_t y) noexcept
{
#if defined(BOOST_JSON_HAS_MSVC_32BIT_INTRINSICS) && !defined(_M_ARM)
    return __emulu(x, y);
#else
    return x * static_cast<std::uint64_t>(y);
#endif
}

[liubing]

#928 doesn't really fix this problem. It should be

#if defined(BOOST_JSON_HAS_MSVC_32BIT_INTRINSICS) && !defined(_M_ARM)

not

#if defined(BOOST_JSON_HAS_MSVC_32BIT_INTRINSICS) && !defined(_M_ARM64)

[mborland]

That's my mistake. The PR has been updated.

[liubing]

Thank you.