[clang] [clang] Implement __builtin_{clzg,ctzg} (PR #83431)

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@@ -662,6 +662,12 @@ def Clz : Builtin, BitShort_Int_Long_LongLongTemplate {
 
 // FIXME: Add int clzimax(uintmax_t)
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overmighty wrote:

Should this FIXME and the `ctzimax(uintmax_t)` one below be removed?

https://github.com/llvm/llvm-project/pull/83431