tidy-up: prefer return over exit(), fix fallouts

To avoid breaking the control flow and align to majority of code
already using `return`.

`exit()` has the side-effect of suppressing leak detection in cases.
Fix fallouts detected after switching to `return`.

- configure:
  - fix `getaddrinfo` run test to call `freeaddrinfo()` to pacify ASAN,
    and call `WSACleanup()` to deinit winsock2.
  - fix `getifaddrs` run test to call `freeifaddrs()` to pacify ASAN.
- tests/server:
  - setup `atexit(win32_cleanup)` via `win32_init()`.
  - return 2 instead of 1 on winsock2 init failures.
  - sws: goto cleanup instead of `exit()` in `http_connect()`.
    Follow-up to 02dfe71937 #7235
- tests/client/http:
  - cleanup memory to pacify ASAN in `h2-upgrade-extreme`,
    `tls-session-reuse`.
- examples:
  - block_ip: fix memory leak reported by CI.
  - http2-upload: avoid handle leaks.

Untouched `exit()` calls, made from callbacks:
- docs/examples: ephiperfifo.c, ghiper.c, hiperfifo.c
- tests/libtest: lib582.c, lib655.c, lib670.c
- tests/server: tftpd.c

Closes #16507

tests/server/mqttd.c

@@ -1018,8 +1018,8 @@ int main(int argc, char *argv[])
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   CURL_SET_BINMODE(stdin);

tests/server/resolve.c

@@ -99,8 +99,8 @@ int main(int argc, char *argv[])
   }
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
 #if defined(CURLRES_IPV6)

tests/server/rtspd.c

@@ -1145,8 +1145,8 @@ int main(int argc, char *argv[])
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   install_signal_handlers(false);

tests/server/sockfilt.c

@@ -1507,8 +1507,8 @@ int main(int argc, char *argv[])
   }
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   CURL_SET_BINMODE(stdin);

tests/server/socksd.c

@@ -1086,8 +1086,8 @@ int main(int argc, char *argv[])
   }
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   CURL_SET_BINMODE(stdin);

tests/server/sws.c

@@ -1611,7 +1611,7 @@ static void http_connect(curl_socket_t *infdp,
           if(!req2) {
             req2 = malloc(sizeof(*req2));
             if(!req2)
-              exit(1);
+              goto http_connect_cleanup;  /* fail */
           }
           memset(req2, 0, sizeof(*req2));
           logmsg("====> Client connect DATA");
@@ -2207,8 +2207,8 @@ int main(int argc, char *argv[])
             is_proxy ? "-proxy" : "", socket_type);
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   install_signal_handlers(false);

tests/server/tftpd.c

@@ -644,8 +644,8 @@ int main(int argc, char **argv)
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
 #ifdef _WIN32
-  win32_init();
-  atexit(win32_cleanup);
+  if(win32_init())
+    return 2;
 #endif
 
   install_signal_handlers(true);

tests/server/util.c

@@ -153,7 +153,17 @@ void win32_perror(const char *msg)
   fprintf(stderr, "%s\n", buf);
 }
 
-void win32_init(void)
+static void win32_cleanup(void)
+{
+#ifdef USE_WINSOCK
+  WSACleanup();
+#endif  /* USE_WINSOCK */
+
+  /* flush buffers of all streams regardless of their mode */
+  _flushall();
+}
+
+int win32_init(void)
 {
 #ifdef USE_WINSOCK
   WORD wVersionRequested;
@@ -166,7 +176,7 @@ void win32_init(void)
   if(err) {
     perror("Winsock init failed");
     logmsg("Error initialising Winsock -- aborting");
-    exit(1);
+    return 1;
   }
 
   if(LOBYTE(wsaData.wVersion) != LOBYTE(wVersionRequested) ||
@@ -174,19 +184,11 @@ void win32_init(void)
     WSACleanup();
     perror("Winsock init failed");
     logmsg("No suitable winsock.dll found -- aborting");
-    exit(1);
+    return 1;
   }
 #endif  /* USE_WINSOCK */
-}
-
-void win32_cleanup(void)
-{
-#ifdef USE_WINSOCK
-  WSACleanup();
-#endif  /* USE_WINSOCK */
-
-  /* flush buffers of all streams regardless of their mode */
-  _flushall();
+  atexit(win32_cleanup);
+  return 0;
 }
 
 /* socket-safe strerror (works on Winsock errors, too) */

tests/server/util.h

@@ -51,8 +51,7 @@ extern const char *cmdfile;
 #define perror(m) win32_perror(m)
 void win32_perror(const char *msg);
 
-void win32_init(void);
-void win32_cleanup(void);
+int win32_init(void);
 const char *sstrerror(int err);
 #else   /* _WIN32 */