Proposed resolution:

This wording is relative to N5032.

[Drafting Note: Two mutually exclusive options are prepared, depicted below by Option A and Option B, respectively.]

Option A:

1. Modify [version.syn] as indicated:

   […]
   #define __cpp_lib_to_string                         202306L202511L // also in <string>
   […]
   

Option B:

1. Modify [version.syn] as indicated:

   […]
   #define __cpp_lib_constexpr_string                  201907L202511L // also in <string>
   […]
   

P3391R2 added `constexpr` to integral overloads of `std::to_string` and `std::to_wstring`. However, the paper only added one feature-test macro `__cpp_lib_constexpr_format`, which doesn't seem clearly related to `std::to_(w)string`.

Given that P3391R2 contained the constexpr additions in P3438R0 which proposed to bump `__cpp_lib_to_string`, perhaps we should bump that FTM. It might be also reasonable to bump `__cpp_lib_constexpr_string` for pure constexpr additions.