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/cf-socket.c

@@ -163,7 +163,8 @@ tcpkeepalive(struct Curl_easy *data,
   /* only set IDLE and INTVL if setting KEEPALIVE is successful */
   if(setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE,
         (void *)&optval, sizeof(optval)) < 0) {
-    infof(data, "Failed to set SO_KEEPALIVE on fd %d", sockfd);
+    infof(data, "Failed to set SO_KEEPALIVE on fd %" CURL_FORMAT_SOCKET_T,
+          sockfd);
   }
   else {
 #if defined(SIO_KEEPALIVE_VALS)
@@ -178,8 +179,9 @@ tcpkeepalive(struct Curl_easy *data,
     vals.keepaliveinterval = optval;
     if(WSAIoctl(sockfd, SIO_KEEPALIVE_VALS, (LPVOID) &vals, sizeof(vals),
                 NULL, 0, &dummy, NULL, NULL) != 0) {
-      infof(data, "Failed to set SIO_KEEPALIVE_VALS on fd %d: %d",
-            (int)sockfd, WSAGetLastError());
+      infof(data, "Failed to set SIO_KEEPALIVE_VALS on fd "
+                  "%" CURL_FORMAT_SOCKET_T ": %d",
+                  sockfd, WSAGetLastError());
     }
 #else
 #ifdef TCP_KEEPIDLE
@@ -187,7 +189,8 @@ tcpkeepalive(struct Curl_easy *data,
     KEEPALIVE_FACTOR(optval);
     if(setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE,
           (void *)&optval, sizeof(optval)) < 0) {
-      infof(data, "Failed to set TCP_KEEPIDLE on fd %d", sockfd);
+      infof(data, "Failed to set TCP_KEEPIDLE on fd %" CURL_FORMAT_SOCKET_T,
+            sockfd);
     }
 #elif defined(TCP_KEEPALIVE)
     /* Mac OS X style */
@@ -195,7 +198,8 @@ tcpkeepalive(struct Curl_easy *data,
     KEEPALIVE_FACTOR(optval);
     if(setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPALIVE,
       (void *)&optval, sizeof(optval)) < 0) {
-      infof(data, "Failed to set TCP_KEEPALIVE on fd %d", sockfd);
+      infof(data, "Failed to set TCP_KEEPALIVE on fd %" CURL_FORMAT_SOCKET_T,
+            sockfd);
     }
 #endif
 #ifdef TCP_KEEPINTVL
@@ -203,7 +207,8 @@ tcpkeepalive(struct Curl_easy *data,
     KEEPALIVE_FACTOR(optval);
     if(setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL,
           (void *)&optval, sizeof(optval)) < 0) {
-      infof(data, "Failed to set TCP_KEEPINTVL on fd %d", sockfd);
+      infof(data, "Failed to set TCP_KEEPINTVL on fd %" CURL_FORMAT_SOCKET_T,
+            sockfd);
     }
 #endif
 #endif
@@ -983,20 +988,14 @@ static CURLcode cf_socket_open(struct Curl_cfilter *cf,
   if(result)
     goto out;
 
-#ifndef CURL_DISABLE_VERBOSE_STRINGS
-  {
-    const char *ipmsg;
 #ifdef ENABLE_IPV6
-    if(ctx->addr.family == AF_INET6) {
-      set_ipv6_v6only(ctx->sock, 0);
-      ipmsg = "  Trying [%s]:%d...";
-    }
-    else
-#endif
-      ipmsg = "  Trying %s:%d...";
-    infof(data, ipmsg, ctx->r_ip, ctx->r_port);
+  if(ctx->addr.family == AF_INET6) {
+    set_ipv6_v6only(ctx->sock, 0);
+    infof(data, "  Trying [%s]:%d...", ctx->r_ip, ctx->r_port);
   }
+  else
 #endif
+    infof(data, "  Trying %s:%d...", ctx->r_ip, ctx->r_port);
 
 #ifdef ENABLE_IPV6
   is_tcp = (ctx->addr.family == AF_INET
@@ -1574,7 +1573,7 @@ static CURLcode cf_socket_query(struct Curl_cfilter *cf,
         *when = ctx->first_byte_at;
         break;
       }
-      /* FALLTHROUGH */
+      FALLTHROUGH();
     default:
       *when = ctx->connected_at;
       break;