[clang] [Clang] Add flags and lang option for C++2d (PR #203992)

[Corentin Jabot via cfe-commits]

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@@ -191,6 +191,19 @@ LANGSTANDARD(gnucxx26, "gnu++2c",
              CPlusPlus20 | CPlusPlus23 | CPlusPlus26 | Digraphs | HexFloat | GNUMode, 202400)
 LANGSTANDARD_ALIAS(gnucxx26, "gnu++26")
 
+// FIXME: Use correct version code for C++29 once published.
+LANGSTANDARD(cxx29, "c++2d",
+             CXX, "Working draft for C++2d",
+             LineComment | CPlusPlus | CPlusPlus11 | CPlusPlus14 | CPlusPlus17 |
+             CPlusPlus20 | CPlusPlus23 | CPlusPlus26 | CPlusPlus29 | Digraphs | HexFloat, 202700)
+LANGSTANDARD_ALIAS(cxx29, "c++29")
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cor3ntin wrote:

I an happy being conservative here - as long as there is _a_ flag, we are good for the time being

https://github.com/llvm/llvm-project/pull/203992