[all-commits] [llvm/llvm-project] 4740e9: [libc++] Improve LIBCXX_ENABLE_INCOMPLETE_FEATURES.

[mordante via All-commits]

  Branch: refs/heads/release/13.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 4740e92e29da0916291f0eed2edc75c4b89df5f5
      https://github.com/llvm/llvm-project/commit/4740e92e29da0916291f0eed2edc75c4b89df5f5
  Author: Mark de Wever <koraq at xs4all.nl>
  Date:   2021-08-02 (Mon, 02 Aug 2021)

  Changed paths:
    M libcxx/include/format
    M libcxx/include/ranges

  Log Message:
  -----------
  [libc++] Improve LIBCXX_ENABLE_INCOMPLETE_FEATURES.

@tcanens pointed out the current behavior of the macro breaks the usage
pattern described in http://wg21.link/SD6
```
```

To support this usage pattern the hard errror is removed. Instead the
header includes nothing but the `<version>` header.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D107134

(cherry picked from commit d618a1cc5c3919d29ee27fa48de80bed4dcb3566)