lib: merge `ENABLE_QUIC` C macro into `USE_HTTP3`

Before this patch `lib/curl_setup.h` defined these two macros right
next to each other, then the source code used them interchangeably.

lib: merge `ENABLE_QUIC` C macro into `USE_HTTP3`

Before this patch `lib/curl_setup.h` defined these two macros right
next to each other, then the source code used them interchangeably.

After this patch, `USE_HTTP3` guards all HTTP/3 / QUIC features.
(Like `USE_HTTP2` does for HTTP/2.) `ENABLE_QUIC` is no longer used.

This patch doesn't change the way HTTP/3 is enabled via autotools
or CMake. Builders who enabled HTTP/3 manually by defining both of
these macros via `CPPFLAGS` can now delete `-DENABLE_QUIC`.

Closes #13352

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lib: add trace support for client reads and writes

- add `CURL_TRC_READ()` and `CURL_TRC_WRITE()`
- use in generic client writers and readers, as well
as http headers, chunking and

lib: add trace support for client reads and writes

- add `CURL_TRC_READ()` and `CURL_TRC_WRITE()`
- use in generic client writers and readers, as well
as http headers, chunking and websockets

Closes #13223

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DoH: add trace configuration

- refs #12397 where it is dicussed how to en-/disable verbose output
of DoH operations
- introducing `struct curl_trc_feat` to track a curl feature for

DoH: add trace configuration

- refs #12397 where it is dicussed how to en-/disable verbose output
of DoH operations
- introducing `struct curl_trc_feat` to track a curl feature for
tracing
- adding `data->state.feat` optionally pointing to the feature a
transfer belongs to
- adding trace functions and verbosity checks on features
- using trace feature in DoH code
- documenting `doh` as feature for `--trace-config`

Closes #12411

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ftp: tracing improvements

- trace socketindex for connection filters when not the first
- trace socket fd in tcp
- trace pollset adjusts in vtls

Closes #12902

build: delete/replace clang warning pragmas

- delete redundant warning suppressions for `-Wformat-nonliteral`.
This now relies on `CURL_PRINTF()` and it's theoratically possible

build: delete/replace clang warning pragmas

- delete redundant warning suppressions for `-Wformat-nonliteral`.
This now relies on `CURL_PRINTF()` and it's theoratically possible
that this macro isn't active but the warning is. We're ignoring this
as a corner-case here.

- replace two pragmas with code changes to avoid the warnings.

Follow-up to aee4ebe59161d0a5281743f96e7738ad97fe1cd4 #12803
Follow-up to 09230127589eccc7e01c1a7217787ef8e64f3328 #12540
Follow-up to 3829759bd042c03225ae862062560f568ba1a231 #12489

Reviewed-by: Daniel Stenberg
Closes #12812

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build: enable missing OpenSSF-recommended warnings, with fixes

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
as of 2023-11-29 [1]

build: enable missing OpenSSF-recommended warnings, with fixes

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
as of 2023-11-29 [1].

Enable new recommended warnings (except `-Wsign-conversion`):

- enable `-Wformat=2` for clang (in both cmake and autotools).
- add `CURL_PRINTF()` internal attribute and mark functions accepting
printf arguments with it. This is a copy of existing
`CURL_TEMP_PRINTF()` but using `__printf__` to make it compatible
with redefinting the `printf` symbol:
https://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_5.html#SEC94
- fix `CURL_PRINTF()` and existing `CURL_TEMP_PRINTF()` for
mingw-w64 and enable it on this platform.
- enable `-Wimplicit-fallthrough`.
- enable `-Wtrampolines`.
- add `-Wsign-conversion` commented with a FIXME.
- cmake: enable `-pedantic-errors` the way we do it with autotools.
Follow-up to d5c0351055d5709da8f3e16c91348092fdb481aa #2747
- lib/curl_trc.h: use `CURL_FORMAT()`, this also fixes it to enable format
checks. Previously it was always disabled due to the internal `printf`
macro.

Fix them:

- fix bug where an `set_ipv6_v6only()` call was missed in builds with
`--disable-verbose` / `CURL_DISABLE_VERBOSE_STRINGS=ON`.
- add internal `FALLTHROUGH()` macro.
- replace obsolete fall-through comments with `FALLTHROUGH()`.
- fix fallthrough markups: Delete redundant ones (showing up as
warnings in most cases). Add missing ones. Fix indentation.
- silence `-Wformat-nonliteral` warnings with llvm/clang.
- fix one `-Wformat-nonliteral` warning.
- fix new `-Wformat` and `-Wformat-security` warnings.
- fix `CURL_FORMAT_SOCKET_T` value for mingw-w64. Also move its
definition to `lib/curl_setup.h` allowing use in `tests/server`.
- lib: fix two wrongly passed string arguments in log outputs.
Co-authored-by: Jay Satiro
- fix new `-Wformat` warnings on mingw-w64.

[1] https://github.com/ossf/wg-best-practices-os-developers/blob/56c0fde3895bfc55c8a973ef49a2572c507b2ae1/docs/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C%2B%2B.md

Closes #12489

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vtls: remove the Curl_cft_ssl_proxy object if CURL_DISABLE_PROXY

Closes #12459

build: variadic macro tidy-ups

- delete unused `HAVE_VARIADIC_MACROS_C99/GCC` feature checks.
(both autotools and CMake.)
- delete duplicate `NULL` check in `Curl_trc_cf_infof()`.

build: variadic macro tidy-ups

- delete unused `HAVE_VARIADIC_MACROS_C99/GCC` feature checks.
(both autotools and CMake.)
- delete duplicate `NULL` check in `Curl_trc_cf_infof()`.
- fix compiler warning in `CURL_DISABLE_VERBOSE_STRINGS` builds.
```
./lib/cf-socket.c:122:41: warning: unused parameter 'data' [-Wunused-parameter]
static void nosigpipe(struct Curl_easy *data,
^
```
- fix `#ifdef` comments in `lib/curl_trc.{c,h}`.
- fix indentation in some `infof()` calls.

Follow-up to dac293cfb7026b1ca4175d88b80f1432d3d3c684 #12167

Cherry-picked from #12105
Closes #12210

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lib: apache style infof and trace macros/functions

- test for a simplified C99 variadic check
- args to infof() in --disable-verbose are no longer disregarded but
must compile.

lib: apache style infof and trace macros/functions

- test for a simplified C99 variadic check
- args to infof() in --disable-verbose are no longer disregarded but
must compile.

Closes #12167
Fixes #12083
Fixes #11880
Fixes #11891

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curl_trc: remove a bad assertion

- Remove DEBUGASSERT that an internal handle must not have user
private_data set before calling the user's debug callback.

This is a follow-up

curl_trc: remove a bad assertion

- Remove DEBUGASSERT that an internal handle must not have user
private_data set before calling the user's debug callback.

This is a follow-up to 0dc40b2a. The user can distinguish their easy
handle from an internal easy handle by setting CURLOPT_PRIVATE on their
easy handle. I had wrongly assumed that meant the user couldn't then
set CURLOPT_PRIVATE on an internal handle as well.

Bug: https://github.com/curl/curl/pull/12060#issuecomment-1754594697
Reported-by: Daniel Stenberg

Closes https://github.com/curl/curl/pull/12104

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CURLOPT_DEBUGFUNCTION.3: warn about internal handles

- Warn that the user's debug callback may be called with the handle
parameter set to an internal handle.

Without this warn

CURLOPT_DEBUGFUNCTION.3: warn about internal handles

- Warn that the user's debug callback may be called with the handle
parameter set to an internal handle.

Without this warning the user may assume that the only handles their
debug callback receives are the easy handles on which they set
CURLOPT_DEBUGFUNCTION.

This is a follow-up to f8cee8cc which changed DoH handles to inherit
the debug callback function set in the user's easy handle. As a result
those handles are now passed to the user's debug callback function.

Closes https://github.com/curl/curl/pull/12034

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trace: make tracing available in non-debug builds

Add --trace-config to curl

Add curl_global_trace() to libcurl

Closes #11421