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
- 'CURL *' handles are called 'curl'
- 'CURLM *' handles are called 'multi'
- write callbacks are called 'write_cb'
- read callbacs are called 'read_cb'
- CURLcode variables are called 'res'
It makes the examples look and feel more consistent. It allows for
easier copy and pasting between examples.
Closes#19299
- add `curl_global_init()` and `curl_global_cleanup()` where missing.
- check the result of `curl_global_init()` where missing.
- return the last curl error from `main()`.
- drop Win32-specific socket initialization in favor of `curl_global_init()`.
- rename some outliers to `res` for curl result code.
- fix cleanup in some error cases.
Inspired by Joshua's report on examples.
Closes#19053
