[llvm-bugs] [Bug 46791] New: SFINAE using void_t causes a redefiniton error

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46791

            Bug ID: 46791
           Summary: SFINAE using void_t causes a redefiniton error
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++17
          Assignee: unassignedclangbugs at nondot.org
          Reporter: denizevrenci 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

https://godbolt.org/z/15ofMv

The source is as follows:
```
#include <array>
#include <type_traits> 

template <typename T, typename = void>
struct indirectly_readable_traits {};

template <typename T>
struct indirectly_readable_traits<T*>
{
    using value_type = std::remove_cv_t<T>;
};

template <typename T>
struct indirectly_readable_traits<T, std::void_t<typename T::value_type>>
{
    using value_type = std::remove_cv_t<typename T::value_type>;
};

template <typename T>
struct indirectly_readable_traits<T, std::void_t<typename T::element_type>>
{
    using value_type = std::remove_cv_t<typename T::element_type>;
};

static_assert(std::is_same_v<typename
indirectly_readable_traits<std::array<int, 5>>::value_type, int>);
```

This compiles both in GCC trunk and MSVC v19.24. Clang terminates compilation
with the following error: "redefinition of 'indirectly_readable_traits<T,
std::void_t<typename T::element_type>>'"

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