Also use the C locale for re-checking our list of tests
Also use the C locale for re-checking our list of tests

otherwise, when the tests directory contains vtc files whose names
get sorted differently in the current environment's locale than in C,
config.status will get re-run for every make check invocation, which
is particularly annoying with parallel makes

feld/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache