locale: Handle loading a missing locale twice (Bug 14247)

locale: Handle loading a missing locale twice (Bug 14247)

Delay setting file->decided until the data has been successfully loaded
by _nl_load_locale().  If the function fails to load the data then we
must return and error and leave decided untouched to allow the caller to
attempt to load the data again at a later time.  We should not set
decided to 1 early in the function since doing so may prevent attempting
to load it again. We want to try loading it again because that allows an
open to fail and set errno correctly.

On the other side of this problem is that if we are called again with
the same inputs we will fetch the cached version of the object and carry
out no open syscalls and that fails to set errno so we must set errno to
ENOENT in that case.  There is a second code path that has to be handled
where the name of the locale matches but the codeset doesn't match.

These changes ensure that errno is correctly set on failure in all the
return paths in _nl_find_locale().

Adds tst-locale-loadlocale to cover the bug.

No regressions on x86_64.

Co-authored-by: Jeff Law <law@redhat.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>