[PATCH] libstdc++: Define feature test macros for hardened implementation

[Jonathan Wakely]

On Fri, 22 May 2026 at 00:40, Jonathan Wakely wrote:
>
> The P3471R4 and P3697R1 proposals adding hardened preconditions also
> defined feature test macros that can be tested to check if the hardened
> preconditions are checked.

You can tell I wrote this in the middle of the night, "tested to check
if [...] are checked".

I've changed it locally to:

   The P3471R4 and P3697R1 proposals adding hardened preconditions also
   defined feature test macros that indicate whether the hardened
   preconditions are checked. For our implementation, those checks are
   enabled by defining _GLIBCXX_ASSERTIONS.