Thank you for the information! In crypto.h.in file I see the following:

# if defined(OPENSSL_THREADS) && !defined(CRYPTO_TDEBUG)
480 #  if defined(_WIN32)
481 #   if defined(BASETYPES) || defined(_WINDEF_H)
482 /* application has to include <windows.h> in order to use this */
483 typedef DWORD CRYPTO_THREAD_LOCAL;
484 typedef DWORD CRYPTO_THREAD_ID;
485
486 typedef LONG CRYPTO_ONCE;
487 #    define CRYPTO_ONCE_STATIC_INIT 0
488 #   endif
489 #  else
490 #   if defined(__TANDEM) && defined(_SPT_MODEL_)
491 #    define  SPT_THREAD_SIGNAL 1
492 #    define  SPT_THREAD_AWARE 1
493 #    include <spthread.h>
494 #   else
495 #    include <pthread.h>
496 #   endif
497 typedef pthread_once_t CRYPTO_ONCE;
498 typedef pthread_key_t CRYPTO_THREAD_LOCAL;
499 typedef pthread_t CRYPTO_THREAD_ID;

We have our own wrappers for the above pthread_once_t, pthread_t. So, we are getting an error in compilation of our code. Could you please let me know how do I avoid this issue with reference to the above openssl variables or any other workaround that is available? In openssl 1.0.2 version these pthread variables were not present. We were using openssl 1.0.2 before. We do not want to declare the above pthread variables of openssl 3.0.15 as we have our own wrappers. Thanks!