[clang] Add typed variants for C23 stdbit.h builtins (#192718)
stdc_leading_zeros_{uc,us,ui,ul,ull}
stdc_leading_ones_{uc,us,ui,ul,ull}
stdc_trailing_zeros_{uc,us,ui,ul,ull}
stdc_trailing_ones_{uc,us,ui,ul,ull}
stdc_first_leading_zero_{uc,us,ui,ul,ull}
stdc_first_leading_one_{uc,us,ui,ul,ull}
stdc_first_trailing_zero_{uc,us,ui,ul,ull}
stdc_first_trailing_one_{uc,us,ui,ul,ull}
stdc_count_zeros_{uc,us,ui,ul,ull}
stdc_count_ones_{uc,us,ui,ul,ull}
stdc_has_single_bit_{uc,us,ui,ul,ull}
stdc_bit_width_{uc,us,ui,ul,ull}
stdc_bit_floor_{uc,us,ui,ul,ull}
stdc_bit_ceil_{uc,us,ui,ul,ull}
Lower type-specific <stdbit.h> functions to LLVM intrinsics
(ctlz/cttz/ctpop). Includes constant expression support and tests for
Sema, CodeGen, and constant evaluation.
Followup:#79630
e535fbfb98