Emacs currently uses the Gnulib headers count-trailing-zeros.h and 
count-one-bits.h to do some low-level bit operations efficiently. C23 
has standardized this in a new header <stdbit.h> and I've recently added 
support for a Gnulib <stdbit.h> substitute, taking implementation ideas 
from count-trailing-zeros.h, count-one-bits.h and elsewhere. So I'm 
planning to switch Emacs to the C23 standard way of doing things, using 
the Gnulib substitute on non-C23 platforms.

The first attached patch does this. I plan to test this somewhat more 
before installing, but thought I'd give people a heads-up.

The second attached patch is a minor cleanup to the 32-bit Android code, 
a cleanup made possible by the first attached patch. This cleanup patch 
is optional of course. By the way, I'm surprised to see the code in 
sfmt.c implementing 64-bit arithmetic from pairs of 32-bit words, as I 
thought even ancient 32-bit Android has 64-bit 'unsigned long long', but 
that's a matter for the Android experts I suppose.