[Bug c/113887] New: no support for %w128 length modifiers

["jens.gustedt at inria dot fr" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113887

            Bug ID: 113887
           Summary: no support for %w128 length modifiers
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jens.gustedt at inria dot fr
  Target Milestone: ---

With C23 and the %w length modifiers and `_BitInt(128)` literals, it will
finally be possible to have `[u]int128_t` types consistently as type aliases
for all architectures where gcc defines the `__int128` types. I am currently
implementing such a support on musl, but unfortunately the %w128 length
modifiers are diagnosed as being wrong.

```
#include <stdio.h>

int main() {
    unsigned __int128 x = 2;
    printf("%w128x\n", x);
}
```