build: fully omit verbose strings and code when disabled

When the compiler supports C99.

- map logging functions to macro stubs when verbose logging is disabled
  and the compiler is C99. Make sure these stubs silence unused variable
  warnings for non-variadic arguments.
  Before this patch they mapped to function stubs, the same codepath
  used for C89 compiler in this configuration.

- introduce new macros to tell the compiler which code to include
  when verbose code is active, or inactive:

  - `CURLVERBOSE`: defined when verbose code is active.
    To enclose blocks of code only used for verbose logging.

  - `VERBOSE(statement);`:
    compile statement when verbose code is active.
    To mark code lines only used for verbose logging.

  - `NOVERBOSE(statement);`:
    compile statement when verbose code is inactive.
    To suppress warnings for arguments passed to logging functions via
    printf masks, e.g. `NOVERBOSE((void)ipaddress);`, yet keeping
    the warning in verbose builds.

  Note these macros are not the same as `CURL_DISABLE_VERBOSE_STRINGS`.
  Verbose code is always active in C89 mode (without variadic macro
  support).

- drop existing uses of `CURL_DISABLE_VERBOSE_STRINGS` where redundant,
  or replace with the above macros. Ending up reducing the number of
  `#ifdef`s, and also the number of lines.

Assisted-by: Daniel Stenberg
Assisted-by: Jay Satiro
Reported-by: Dan Fandrich
Fixes #20341
Refs: #12105 #12167

Closes #20353

lib/multi_ev.c

@@ -195,6 +195,7 @@ static CURLMcode mev_forget_socket(struct Curl_multi *multi,
 
   /* We managed this socket before, tell the socket callback to forget it. */
   if(entry->announced && multi->socket_cb) {
+    NOVERBOSE((void)cause);
     CURL_TRC_M(data, "ev %s, call(fd=%" FMT_SOCKET_T ", ev=REMOVE)", cause, s);
     mev_in_callback(multi, TRUE);
     rc = multi->socket_cb(data, s, CURL_POLL_REMOVE,