openssl: x509: allow build with OpenSSL 4.x

[heitbaum]

ASN1_STRING are now opaque types — the internal data and length fields are no longer directly accessible. Use the accessor API instead. Accessors have been available since OpenSSL 1.1.0

Signatures of numerous API functions, including those that are related to X509 processing, are changed to include const qualifiers for argument and return types, where suitable. Add const qualifer to variables.

fixes:

../lib/tls/openssl/openssl-x509.c: In function 'lws_tls_openssl_asn1time_to_unix':
../lib/tls/openssl/openssl-x509.c:42:41: error: invalid use of incomplete typedef 'ASN1_TIME' {aka 'struct asn1_string_st'}
   42 |         const char *p = (const char *)as->data;
      |                                         ^~
../lib/tls/openssl/openssl-x509.c: In function 'lws_tls_openssl_cert_info':
../lib/tls/openssl/openssl-x509.c:129:20: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  129 |                 xn = X509_get_subject_name(x509);
      |                    ^
../lib/tls/openssl/openssl-x509.c:148:20: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  148 |                 xn = X509_get_issuer_name(x509);
      |                    ^
../lib/tls/openssl/openssl-x509.c:218:21: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  218 |                 ext = X509_get_ext(x509, (int)loc);
      |                     ^
../lib/tls/openssl/openssl-x509.c:229:48: error: invalid use of incomplete typedef 'ASN1_OCTET_STRING' {aka 'struct asn1_string_st'}
  229 |                 dp = (const unsigned char *)val->data;
      |                                                ^~
../lib/tls/openssl/openssl-x509.c:230:27: error: invalid use of incomplete typedef 'ASN1_OCTET_STRING' {aka 'struct asn1_string_st'}
  230 |                 xlen = val->length;
      |                           ^~
../lib/tls/openssl/openssl-x509.c:246:21: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  246 |                 ext = X509_get_ext(x509, (int)loc);
      |                     ^
../lib/tls/openssl/openssl-x509.c:303:21: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  303 |                 ext = X509_get_ext(x509, (int)loc);
      |                     ^
../lib/tls/openssl/openssl-x509.c:329:21: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  329 |                 ext = X509_get_ext(x509, (int)loc);
      |                     ^
../lib/tls/openssl/openssl-x509.c:333:21: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  333 |                 val = X509_EXTENSION_get_data(ext);
      |                     ^
../lib/tls/openssl/openssl-x509.c:340:48: error: invalid use of incomplete typedef 'ASN1_OCTET_STRING' {aka 'struct asn1_string_st'}
  340 |                 dp = (const unsigned char *)val->data;
      |                                                ^~
../lib/tls/openssl/openssl-x509.c:343:55: error: invalid use of incomplete typedef 'ASN1_OCTET_STRING' {aka 'struct asn1_string_st'}
  343 |                                     &tag, &xclass, val->length) & 0x80)
      |                                                       ^~
../lib/tls/openssl/openssl-x509.c: In function 'lws_x509_verify':
../lib/tls/openssl/openssl-x509.c:459:33: error: initialization discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  459 |                 X509_NAME *xn = X509_get_subject_name(x509->cert);
      |                                 ^~~~~~~~~~~~~~~~~~~~~