doc: Update for glibc 2.42. * doc/glibc-functions/uabs.texi: New file. * doc/glibc-functions/ulabs.texi: New file. * doc/glibc-functions/ullabs.texi: New file. * doc/glibc-functions/uimaxabs.texi: New file. * doc/gnulib.texi (Glibc inttypes.h): New section. (Glibc stdlib.h): Include three of these files.