This adds support for .check files inside the tests directory. .check
files are tests designed to be run with littlecheck.
Port printf test to littlecheck and remove the printf.in test.
POSIX dictates here that incomplete conversions, like in
printf %d\n 15.2
or
printf %d 14g
are still printed along with any error.
This seems alright, as it allows users to silence stderr to accept incomplete conversions.
This commit implements it, but what's a bit weird is the ordering between stdout and stderr,
causing the error to be printed _after_, like
15
14
15.1: value not completely converted
14,2: value not completely converted
but that seems like a general issue with how we buffer the streams.
(I know that nonfatal_error is a copy of most of fatal_error - I tried
differently, and va_* is weird)
Fixes#5532.
This removes the caret as a shorthand for redirecting stderr.
Note that stderr may be redirected to a file via 2>/some/path...
and may be redirected with a pipe via 2>|.
Fixes#4394
Another dev noticed that tests/printf.in was failing because they didn't have
the fr_FR.UTF-8 locale installed. Make that test more resilient by trying
other locales and if no suitable locale is found skipping the test.