[clang] [Clang] Allow __builtin_fma/fmaf/fmal to be used in a constant expression (PR #158048)

[Chaitanya Koparkar via cfe-commits]

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@@ -199,7 +199,7 @@ def FloorF16F128 : Builtin, F16F128MathTemplate {
 
 def FmaF16F128 : Builtin, F16F128MathTemplate {
   let Spellings = ["__builtin_fma"];
-  let Attributes = [FunctionWithBuiltinPrefix, NoThrow, ConstIgnoringErrnoAndExceptions];
+  let Attributes = [FunctionWithBuiltinPrefix, NoThrow, ConstIgnoringErrnoAndExceptions, Constexpr];
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ckoparkar wrote:

I needed to make the _other_ `fma` builtin constexpr, d'oh.

https://github.com/llvm/llvm-project/pull/158048