[Clang] Variable template partial specialization cannot specialize primary template with `auto` NTTP

[MagentaTreehouse]

Reproducer:

template <auto> constexpr bool b = false;
template <int I> constexpr bool b<I> = true; 

Error:

<source>:2:33: error: variable template partial specialization does not specialize any template argument; to define the primary template, remove the template argument list
    2 | template <int I> constexpr bool b<I> = true;
      |                                 ^~~~

Possibly related: #42421.

See Compiler Explorer: https://godbolt.org/z/nEdbcKqWs

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (MagentaTreehouse)

Reproducer: ```c++ template <auto> constexpr bool b = false; template <int I> constexpr bool b<I> = true; ```

Error:

<source>:2:33: error: variable template partial specialization does not specialize any template argument; to define the primary template, remove the template argument list
    2 | template <int I> constexpr bool b<I> = true;
      |                                 ^~~~

Possibly related: #42421.

See Compiler Explorer: https://godbolt.org/z/nEdbcKqWs

[shafik]

edg also agrees w/ gcc/MSVS: https://godbolt.org/z/MqE54KnfM

[hubert-reinterpretcast]

This is a bug. The equivalent class template partial specialization case does work with Clang.