C23's <stdbit.h> in the long run should be better supported than
Gnulib's count-one-bits.h and similar headers, so switch to the
C23 primitives, with a Gnulib fallback for platforms lacking C23.
* admin/merge-gnulib (GNULIB_MODULES): Remove count-leading-zeros,
count-one-bits, count-trailing-zeros. Add stdc_bit_width,
stdc_count_ones, stdc_trailing_zeros.
* lib/count-leading-zeros.c, lib/count-leading-zeros.h:
* lib/count-one-bits.c, lib/count-one-bits.h:
* lib/count-trailing-zeros.c, lib/count-trailing-zeros.h: Remove.
* lib/stdbit.c, lib/stdbit.in.h, lib/stdc_bit_width.c:
* lib/stdc_count_ones.c, lib/stdc_leading_zeros.c:
* lib/stdc_trailing_zeros.c, m4/stdbit_h.m4:
New files, copied from Gnulib.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* src/data.c: Do not include count-one-bits.h, count-trailing-zeros.h.
Instead, rely on lisp.h including stdbit.h.
(Flogcount, Fbool_vector_count_population)
(Fbool_vector_count_consecutive): Use stdbit.h macros instead of
count-one-bits.h and count-trailing-zeros.h macros.
(shift_right_ull, count_one_bits_word, pre_value)
(count_trailing_zero_bits): Remove; no longer needed.
* src/lisp.h: Include stdbit.h instead of count-leading-zeros.h.
(elogb): Use stdbit.h macro instead of count-leading-zeros.h macro.
