This is an implementation of a CURLOPT_WRITEFUNCTION callback that just
throws away the content and returns success. Saves us from having to
reimplement it many times in different tests.
Closes#21971
Adjust code to avoid `-Wformat-signedness` warnings, while making sure
that enums are always cast to a known type when passing them to `printf`
functions, to support compilers and compiler settings where enums are
not default-size signed ints.
- cast integers printed as hex to `unsigned`. (63 times, 20 of them in
`mbedtls.c`)
- cast misc enums to `int` for printing. (31 times)
- cast `CURL_LOCK_DATA_*` enums to `int`. (4 times)
- cast `CURL_FORMADD_*` enums to `int`. (13 times)
- cast `CURLSHE_*` enums to `int`. (3 times)
- cast `CURLUE_*` enums to `int`. (33 times)
- cast `CURLMSG_*` enums to `int`. (6 times)
- cast `CURLE_*` enums to `int`. (~380 times)
- unit1675: fix mask.
Follow-up to 7c34365cce#21879
Ref: #18343 (initial attempt)
Closes#20848
