wolfssl: fix unused variable warning

[vszakats]

E.g. when building against msys2-mingw wolfssl:
https://packages.msys2.org/base/mingw-w64-wolfssl

lib/vtls/wolfssl.c: In function 'wssl_verify_pinned':
lib/vtls/wolfssl.c:1534:20: error: unused variable 'wssl' [-Werror=unused-variable]
   struct wssl_ctx *wssl = (struct wssl_ctx *)connssl->backend;
                    ^~~~

Ref: https://github.com/curl/curl/actions/runs/13713131802/job/38353245932#step:10:78

Building with the MSYS2 wolfssl is broken due to further issues.

[vszakats]

MSYS2 wolfssl fails with curl:

D:/a/curl/curl/lib/vtls/wolfssl.c: In function 'wssl_vtls_new_session_cb':
D:/a/curl/curl/lib/vtls/wolfssl.c:483:30: error: implicit declaration of function 'wolfSSL_get_app_data'; did you mean 'wolfSSL_get_ex_data'? [-Wimplicit-function-declaration]
   cf = (struct Curl_cfilter*)wolfSSL_get_app_data(ssl);
                              ^~~~~~~~~~~~~~~~~~~~
                              wolfSSL_get_ex_data
D:/a/curl/curl/lib/vtls/wolfssl.c:483:30: error: nested extern declaration of 'wolfSSL_get_app_data' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c:483:8: error: cast from function call of type 'int' to non-matching type 'struct Curl_cfilter *' [-Werror=bad-function-cast]
   cf = (struct Curl_cfilter*)wolfSSL_get_app_data(ssl);
        ^
D:/a/curl/curl/lib/vtls/wolfssl.c:483:8: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
D:/a/curl/curl/lib/vtls/wolfssl.c: In function 'wssl_x509_share_free':
D:/a/curl/curl/lib/vtls/wolfssl.c:706:5: error: implicit declaration of function 'wolfSSL_X509_STORE_free'; did you mean 'wolfSSL_X509_STORE_CTX_free'? [-Wimplicit-function-declaration]
     wolfSSL_X509_STORE_free(share->store);
     ^~~~~~~~~~~~~~~~~~~~~~~
     wolfSSL_X509_STORE_CTX_free
D:/a/curl/curl/lib/vtls/wolfssl.c:706:5: error: nested extern declaration of 'wolfSSL_X509_STORE_free' [-Werror=nested-externs]
[ 33%] Generating CURLOPT_XFERINFOFUNCTION.3, CURLOPT_XOAUTH2_BEARER.3, CURLSHOPT_LOCKFUNC.3, CURLSHOPT_SHARE.3, CURLSHOPT_UNLOCKFUNC.3, CURLSHOPT_UNSHARE.3, CURLSHOPT_USERDATA.3
D:/a/curl/curl/lib/vtls/wolfssl.c: In function 'wssl_set_cached_x509_store':
D:/a/curl/curl/lib/vtls/wolfssl.c:786:6: error: implicit declaration of function 'wolfSSL_X509_STORE_up_ref'; did you mean 'wolfSSL_X509_STORE_CTX_free'? [-Wimplicit-function-declaration]
   if(wolfSSL_X509_STORE_up_ref(store)) {
      ^~~~~~~~~~~~~~~~~~~~~~~~~
      wolfSSL_X509_STORE_CTX_free
D:/a/curl/curl/lib/vtls/wolfssl.c:786:6: error: nested extern declaration of 'wolfSSL_X509_STORE_up_ref' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c: In function 'Curl_wssl_setup_x509_store':
D:/a/curl/curl/lib/vtls/wolfssl.c:831:6: error: implicit declaration of function 'wolfSSL_CTX_get_cert_store'; did you mean 'wolfSSL_CTX_get_mode'? [-Wimplicit-function-declaration]
      wolfSSL_CTX_get_cert_store(wssl->ssl_ctx) == cached_store) {
      ^~~~~~~~~~~~~~~~~~~~~~~~~~
      wolfSSL_CTX_get_mode
D:/a/curl/curl/lib/vtls/wolfssl.c:831:6: error: nested extern declaration of 'wolfSSL_CTX_get_cert_store' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c:831:48: error: comparison between pointer and integer
      wolfSSL_CTX_get_cert_store(wssl->ssl_ctx) == cached_store) {
                                                ^~
D:/a/curl/curl/lib/vtls/wolfssl.c:835:5: error: implicit declaration of function 'wolfSSL_CTX_set_cert_store'; did you mean 'wolfSSL_CTX_save_cert_cache'? [-Wimplicit-function-declaration]
     wolfSSL_CTX_set_cert_store(wssl->ssl_ctx, cached_store);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~
     wolfSSL_CTX_save_cert_cache
D:/a/curl/curl/lib/vtls/wolfssl.c:835:5: error: nested extern declaration of 'wolfSSL_CTX_set_cert_store' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c:840:33: error: implicit declaration of function 'wolfSSL_X509_STORE_new'; did you mean 'wolfSSL_X509_STORE_CTX_new'? [-Wimplicit-function-declaration]
     WOLFSSL_X509_STORE *store = wolfSSL_X509_STORE_new();
                                 ^~~~~~~~~~~~~~~~~~~~~~
                                 wolfSSL_X509_STORE_CTX_new
D:/a/curl/curl/lib/vtls/wolfssl.c:840:33: error: nested extern declaration of 'wolfSSL_X509_STORE_new' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c:840:33: error: initialization makes pointer from integer without a cast [-Wint-conversion]
[ 33%] Built target generate-curl.1
D:/a/curl/curl/lib/vtls/wolfssl.c:854:32: error: initialization makes pointer from integer without a cast [-Wint-conversion]
    WOLFSSL_X509_STORE *store = wolfSSL_CTX_get_cert_store(wssl->ssl_ctx);
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/curl/curl/lib/vtls/wolfssl.c: In function 'Curl_wssl_ctx_init':
D:/a/curl/curl/lib/vtls/wolfssl.c:1117:11: error: implicit declaration of function 'wolfSSL_CTX_set1_curves_list'; did you mean 'wolfSSL_CTX_set_cipher_list'? [-Wimplicit-function-declaration]
       if(!wolfSSL_CTX_set1_curves_list(wctx->ssl_ctx, curves)) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
           wolfSSL_CTX_set_cipher_list
D:/a/curl/curl/lib/vtls/wolfssl.c:1117:11: error: nested extern declaration of 'wolfSSL_CTX_set1_curves_list' [-Werror=nested-externs]
D:/a/curl/curl/lib/vtls/wolfssl.c:1288:3: error: implicit declaration of function 'wolfSSL_set_app_data'; did you mean 'wolfSSL_set_ex_data'? [-Wimplicit-function-declaration]
   wolfSSL_set_app_data(wctx->ssl, ssl_user_data);
   ^~~~~~~~~~~~~~~~~~~~
   wolfSSL_set_ex_data
D:/a/curl/curl/lib/vtls/wolfssl.c:1288:3: error: nested extern declaration of 'wolfSSL_set_app_data' [-Werror=nested-externs]

https://github.com/curl/curl/actions/runs/13713131802/job/38353245932#step:10:20