After this patch, the codebase no longer overrides system printf
functions. Instead it explicitly calls either the curl printf functions
`curl_m*printf()` or the system ones using their original names.
Also:
- drop unused `curl_printf.h` includes.
- checksrc: ban system printf functions, allow where necessary.
Follow-up to db98daab05#18844
Follow-up to 4deea9396b#18814Closes#18866
This uses c-ares under the hood and supports the CURL_DNS_SERVER
environment variable - for debug builds only. The getaddrinfo()
replacement function is only used if CURL_DNS_SERVER is set to make a
debug build work more like a release version without the variable set.
'override-dns' is a new feature for the test suite when curl can be told
to use a dedicated DNS server, and test 2102 is the first to require
this.
Requires c-ares 1.26.0 or later.
Closes#17134
