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/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);