P3748R0: Inspecting `exception_ptr` should be constexpr

[frederick-vs-ja]

Link: https://wg21.link/P3748R0

Feature-test macro (also covers P2927R3):

#define __cpp_lib_exception_ptr_cast 202506L // also in <exception>

I suspect that compiler support is necessary.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: A. Jiang (frederick-vs-ja)

**Link:** https://wg21.link/P3748R0

Feature-test macro (also covers P2927R3):

#define __cpp_lib_exception_ptr_cast 202506L // also in <exception>

I suspect that compiler support is necessary.