[ADT] Add llvm::countr_zero_constexpr#164188

kazutakahirata merged 3 commits intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_20251019_ADT_bit_countr_zero_constexpr_ConstantLog2kazutakahirata/llvm-project:cleanup_20251019_ADT_bit_countr_zero_constexpr_ConstantLog2Copy head branch name to clipboard