maint: replace each "for (;;)" with "while (true)"

maint: replace each "for (;;)" with "while (true)"

Run this command:
  git ls-files | grep '\.[ch]$' \
    | xargs perl -pi -e 's/for \(;;\)/while (true)/g'
...except for randint.c, which does not include stdbool.h.
In that case, use "while (1)".
* gl/lib/randint.c (randint_genmax): Use "while (1)" for infloops.
* src/cat.c (simple_cat, cat): Use "while (true)" for infloops.
* gl/lib/randread.c (readsource, readisaac): Likewise.
* src/copy.c (copy_reg): Likewise.
* src/csplit.c (record_line_starts, process_regexp): Likewise.
* src/cut.c (set_fields): Likewise.
* src/dd.c (iread, parse_symbols): Likewise.
* src/df.c (find_mount_point, main): Likewise.
* src/du.c (main): Likewise.
* src/expand.c (expand): Likewise.
* src/factor.c (factor_using_division, do_stdin): Likewise.
* src/fmt.c (get_space): Likewise.
* src/ls.c (decode_switches): Likewise.
* src/od.c (main): Likewise.
* src/pr.c (main, read_line): Likewise.
* src/shred.c (dopass, genpattern): Likewise.
* src/sort.c (initbuf, fillbuf, getmonth, keycompare): Likewise.
* src/split.c (bytes_split, lines_split): Likewise.
* src/tac.c (tac_seekable): Likewise.
* src/test.c (and, or): Likewise.
* src/tr.c (squeeze_filter, main): Likewise.
* src/tsort.c (search_item): Likewise.
* src/unexpand.c (unexpand): Likewise.
* src/uniq.c (main): Likewise.
* src/yes.c (main): Likewise.