curl: fix integer constant typechecks with curl_easy_setopt()

curl: fix integer constant typechecks with curl_easy_setopt()

The curl documentation specifies that curl_easy_setopt() takes either:

  ...a long, a function pointer, an object pointer or a curl_off_t,
  depending on what the specific option expects.

But when we pass an integer constant like "0", it will by default be a
regular non-long int. This has always been wrong, but seemed to work in
practice (I didn't dig into curl's implementation to see whether this
might actually be triggering undefined behavior, but it seems likely and
regardless we should do what the docs say).

This is especially important since curl has a type-checking macro that
causes building against curl 8.14 to produce many warnings. The specific
commit is due to their 79b4e56b3 (typecheck-gcc.h: fix the typechecks,
2025-04-22). Curiously, it does only seem to trigger when compiled with
-O2 for me.

We can fix it by just marking the constants with a long "L".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>