Fix build with opaque HMAC_CTX in LibreSSL 3.5.

Index: lib_pypy/_cffi_ssl/_cffi_src/openssl/hmac.py
--- lib_pypy/_cffi_ssl/_cffi_src/openssl/hmac.py.orig
+++ lib_pypy/_cffi_ssl/_cffi_src/openssl/hmac.py
@@ -24,7 +24,7 @@ void Cryptography_HMAC_CTX_free(HMAC_CTX *ctx);
 
 CUSTOMIZATIONS = """
 HMAC_CTX *Cryptography_HMAC_CTX_new(void) {
-#if CRYPTOGRAPHY_OPENSSL_110_OR_GREATER
+#if CRYPTOGRAPHY_OPENSSL_110_OR_GREATER || defined(LIBRESSL_VERSION_NUMBER)
     return HMAC_CTX_new();
 #else
     /* This uses OPENSSL_zalloc in 1.1.0, which is malloc + memset */
@@ -36,7 +36,7 @@ HMAC_CTX *Cryptography_HMAC_CTX_new(void) {
 
 
 void Cryptography_HMAC_CTX_free(HMAC_CTX *ctx) {
-#if CRYPTOGRAPHY_OPENSSL_110_OR_GREATER
+#if CRYPTOGRAPHY_OPENSSL_110_OR_GREATER || defined(LIBRESSL_VERSION_NUMBER)
     return HMAC_CTX_free(ctx);
 #else
     if (ctx != NULL) {