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 d5c0351055 #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] 56c0fde389/docs/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C%2B%2B.md

Closes #12489

lib/mprintf.c

@@ -365,7 +365,7 @@ static int dprintf_Pass1(const char *format, struct va_stack *vto,
         case '0':
           if(!(flags & FLAGS_LEFT))
             flags |= FLAGS_PAD_NIL;
-          /* FALLTHROUGH */
+          FALLTHROUGH();
         case '1': case '2': case '3': case '4':
         case '5': case '6': case '7': case '8': case '9':
           flags |= FLAGS_WIDTH;
@@ -385,6 +385,7 @@ static int dprintf_Pass1(const char *format, struct va_stack *vto,
           break;
         case '\0':
           fmt--;
+          FALLTHROUGH();
         default:
           break;
         }
@@ -401,7 +402,7 @@ static int dprintf_Pass1(const char *format, struct va_stack *vto,
       switch(*fmt) {
       case 'S':
         flags |= FLAGS_ALT;
-        /* FALLTHROUGH */
+        FALLTHROUGH();
       case 's':
         vto[i].type = FORMAT_STRING;
         break;