[clang] [clang][doc] Document C2y flags (PR #138521)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Raul Tambre (tambry)

<details>
<summary>Changes</summary>

As discussed at https://github.com/llvm/llvm-project/pull/138459#issuecomment-2850716184

---
Full diff: https://github.com/llvm/llvm-project/pull/138521.diff


2 Files Affected:

- (modified) clang/docs/CommandGuide/clang.rst (+8) 
- (modified) clang/include/clang/Basic/LangStandards.def (+1-1) 


``````````diff
diff --git a/clang/docs/CommandGuide/clang.rst b/clang/docs/CommandGuide/clang.rst
index e3399d39bf00c..1b8776c5e9ad2 100644
--- a/clang/docs/CommandGuide/clang.rst
+++ b/clang/docs/CommandGuide/clang.rst
@@ -155,6 +155,14 @@ Language Selection and Mode Options
 
    ISO C 2023 with GNU extensions
 
+  | ``c2y``
+
+   ISO C 202y
+
+  | ``gnu2y``
+
+   ISO C 202y with GNU extensions
+
  The default C language standard is ``gnu17``, except on PS4, where it is
  ``gnu99``.
 
diff --git a/clang/include/clang/Basic/LangStandards.def b/clang/include/clang/Basic/LangStandards.def
index 49cd9881829d4..244692ab4296a 100644
--- a/clang/include/clang/Basic/LangStandards.def
+++ b/clang/include/clang/Basic/LangStandards.def
@@ -105,7 +105,7 @@ LANGSTANDARD(c2y, "c2y",
 LANGSTANDARD(gnu2y, "gnu2y",
              C, "Working Draft for ISO C2y with GNU extensions",
              LineComment | C99 | C11 | C17 | C23 | C2y | Digraphs | GNUMode | HexFloat)
-
+// TODO: Add the iso9899:202y alias once ISO publishes the standard.
 
 // C++ modes
 LANGSTANDARD(cxx98, "c++98",

``````````

</details>


https://github.com/llvm/llvm-project/pull/138521