The compiler extension is also available in GCC at least, and it was you who cited extensions.
replyDoesn't change the fact that isn't on ISO C.
replyAt least WG21 eventually did the correct thing and placed those extensions into the standard, even if due to governmental pressure.
Also while enabling bounds checking has been a common configuration option in all C++ compilers, clang and GCC aren't all C compilers.
This kind of discussion is also quite telling that nothing will change on WG14, maybe eventually who knows, C2y might finally get fat pointers if voted in, and then we will see during the following decades whatever fruits that will bare.
That WG21 made finally made its containers safer is great, but the C standard library does not have containers. You can still have your own bounds checked containers just fine in C, as you could in the past.. ISO C simply does not matter as much as you like to pretend - for trolling I must assume.
replyWhen we will have a standard for bounds checking arrays and pointers remains to be seen, but this does not stop anyone from using the non-standard tools available today.