[libunwind] [Clang] Add __builtin_vectorelements to get number of elements in vector (PR #69010)

[Erich Keane via cfe-commits]

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@@ -5126,6 +5126,14 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
       Diags.Report(DiagID);
       return;
     }
+    case UETT_VectorElements: {
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erichkeane wrote:

OK, SGTM at least, I just know this pattern of 'cannot yet mangle...' shows up primarily in the MicrosoftMangle, so figured it might need to be covered.  There is some funny-business as to how much each mangles of expressions in template arguments.

This gets me thinking further though,the constexprness of this likely means you may need to mangle this.  I'm open if others are to letting it be done in a follow-up however.

https://github.com/llvm/llvm-project/pull/69010