[libc++][format] Add a CMake Unicode option.
This option is used to select between the format headers output column
width option. This option should be independent of the locale setting.
It's encouraged to default to Unicode unless the platform doesn't offer
that option.
[format.string.std]/10
```
For the purposes of width computation, a string is assumed to be in a
locale-independent, implementation-defined encoding. Implementations
should use a Unicode encoding on platforms capable of displaying Unicode
```
Reviewed By: #libc, ldionne, vitaut
Differential Revision: https://reviews.llvm.org/D103379
NOKEYCHECK=True
GitOrigin-RevId: df2af9936ca096d5bfbf3395c661c2d5a354f673
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index f8b428c..65ef26b 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -42,6 +42,9 @@
is incomplete. Some functions are known to be inefficient; both in memory
usage and performance. The implementation is considered experimental and isn't
considered ABI stable.
+- There's a new CMake option ``LIBCXX_ENABLE_UNICODE`` to disable Unicode
+ support in the ``<format>`` header. This only affects the estimation of the
+ output width of the format functions.
API Changes
-----------