[clang] [clang] Implement `__builtin_is_implicit_lifetime()` (PR #101807)

[Aaron Ballman via cfe-commits]

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@@ -5637,6 +5638,27 @@ static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT,
     return false;
   case UTT_IsTriviallyEqualityComparable:
     return isTriviallyEqualityComparableType(Self, T, KeyLoc);
+  case UTT_IsImplicitLifetime: {
+    DiagnoseVLAInCXXTypeTrait(Self, TInfo,
+                              tok::kw___builtin_is_implicit_lifetime);
+    QualType UnqualT = T->getCanonicalTypeUnqualified();
+    if (UnqualT->isScalarType())
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AaronBallman wrote:

We definitely have to support (some) extensions, but hopefully they shouldn't be too onerous. Things like extended scalar types (all the various floating-point types, int128_t, etc) and vector types have to be supported. But also things like `_Complex`, sizeless types, zero-sized arrays, flexible array members in structures, etc.

https://github.com/llvm/llvm-project/pull/101807