diagnose too-large numbers better

Following on from commit v8.23-82-gaddae94, consistently diagnose
numbers that are too large, so as to distinguish from other errors,
and make the limits obvious.

* gl/modules/xdectoint: A new module implementing xdecto[iu]max(),
which handles the common case of parsing a bounded integer and
exiting with a diagnostic on error.
* gl/lib/xdectoimax.c: The signed variant.
* gl/lib/xdectoint.c: The parameterized implementation.
* gl/lib/xdectoint.h: The interface.
* gl/lib/xdectoumax.c: The unsigned variant.
* bootstrap.conf: Reference the new module.
* cfg.mk (exclude_file_name_regexp--sc_require_config_h_first):
Exclude the parameterized templates.
* src/csplit.c: Output EOVERFLOW or ERANGE errors if appropriate.
* src/fmt.c: Likewise.
* src/fold.c: Likewise.
* src/head.c: Likewise.
* src/ls.c: Likewise.
* src/nl.c: Likewise.
* src/nproc.c: Likewise.
* src/shred.c: Likewise.
* src/shuf.c: Likewise.
* src/stdbuf.c: Likewise.
* src/stty.c: Likewise.
* src/tail.c: Likewise.
* src/truncate.c: Likewise.
* src/split.c: Likewise.
* src/pr.c: Likewise.
* tests/pr/pr-tests.pl: Adjust to avoid matching errno diagnostic.
* tests/fmt/base.pl: Likewise.
* tests/split/l-chunk.sh: Likewise.
* tests/misc/shred-negative.sh: Likewise.
* tests/misc/tail.pl: Likewise.  Also remove the redundant
existing ERR_SUBST from test err-6.
* tests/ls/hex-option.sh: Check HEX/OCT options.
* tests/misc/shred-size.sh: Likewise.
* tests/misc/stty-row-col.sh: Likewise.