[libcxx-commits] [libcxx] [libc++] Add __iswctype to the locale base API since it's required by <locale> (PR #122168)

[Nico Weber via libcxx-commits]

nico wrote:

> > (The Fuchsia problem also blocks updating libc++ in Chromium.)
> 
> What issue are _you_ running into? I'd expect the usual Linux path doesn't suffer from the problem reported by Fuchsia or we would have seen it in our CI?

We build Chromium for Fuchsia.

https://ci.chromium.org/ui/p/chromium/builders/try/fuchsia-x64-cast-receiver-rel/892111/overview

```
[3755/97772] CXX obj/base/third_party/double_conversion/double_conversion/string-to-double.o
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/base/third_party/double_conversion/double_conversion/string-to-double.o....(too long)
In file included from ../../base/third_party/double_conversion/double-conversion/string-to-double.cc:29:
In file included from ../../third_party/libc++/src/include/locale:208:
In file included from ../../third_party/libc++/src/include/__locale:14:
../../third_party/libc++/src/include/__locale_dir/locale_base_api.h:197:10: error: use of undeclared identifier 'iswctype_l'
  197 |   return iswctype_l(__ch, __type, __loc);
      |          ^
1 error generated.
```

https://github.com/llvm/llvm-project/pull/122168