test-check-code: do not use xargs
We have too many files, and passing them via arguments could cause strange
errors on some platforms [1]. Since check-code.py can now take "-" and read
file names from stdin, use it instead of xargs to avoid the argv size limit.
[1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/096346.html
#!/bin/sh
HGENCODING=UTF-8
export HGENCODING
echo ".. -*- coding: utf-8 -*-" > gendoc.txt
echo "" >> gendoc.txt
LANGUAGE=$1 python "$TESTDIR/../doc/gendoc.py" >> gendoc.txt 2> /dev/null || exit
echo "checking for parse errors"
python "$TESTDIR/../doc/docchecker" gendoc.txt
python "$TESTDIR/../doc/runrst" html gendoc.txt /dev/null