add_to_index(): convert forgotten HASH_RENORMALIZE check

add_to_index(): convert forgotten HASH_RENORMALIZE check

Commit 9e5da3d055 (add: use separate ADD_CACHE_RENORMALIZE flag,
2019-01-17) switched out using HASH_RENORMALIZE in our flags field for a
new ADD_CACHE_RENORMALIZE flag. However, it forgot to convert one of the
checks for HASH_RENORMALIZE into the new flag, which totally broke "git
add --renormalize".

To make matters even more confusing, the resulting code would racily
pass the tests!  The forgotten check was responsible for defeating the
up-to-date check of the index entry. That meant that "git add
--renormalize" would refuse to renormalize things that appeared
stat-clean. But most of the time the test commands run fast enough that
the file mtime is the same as the index mtime. And thus we err on the
conservative side and re-hash the file, which is what "--renormalize"
would have wanted.

But if you're unlucky and cross that one-second boundary between writing
the file and writing the index (which is more likely to happen on a slow
or heavily-loaded system), then the file appears stat-clean. And
"--renormalize" would effectively do nothing.

The fix is straightforward: convert this check to use the right flag.

Noticed-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>