Let autoconf detect presence of EVP_MD_CTX_new

Fixes LibreSSL compatibility

configure.ac

@@ -832,6 +832,13 @@ else
   fi
 fi
 
+save_CXXFLAGS="${CXXFLAGS}"
+CXXFLAGS="${CXXFLAGS} ${CRYPTO_CFLAGS} ${SSL_CFLAGS}"
+AC_CHECK_DECLS([EVP_MD_CTX_new],,,[AC_INCLUDES_DEFAULT
+#include <openssl/x509_vfy.h>
+])
+CXXFLAGS="${save_CXXFLAGS}"
+
 dnl univalue check
 
 need_bundled_univalue=yes

src/qt/paymentrequestplus.cpp

@@ -159,7 +159,7 @@ bool PaymentRequestPlus::getMerchant(X509_STORE* certStore, QString& merchant) c
         std::string data_to_verify;                     // Everything but the signature
         rcopy.SerializeToString(&data_to_verify);
 
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#if HAVE_DECL_EVP_MD_CTX_NEW
         EVP_MD_CTX *ctx = EVP_MD_CTX_new();
         if (!ctx) throw SSLVerifyError("Error allocating OpenSSL context.");
 #else
@@ -174,7 +174,7 @@ bool PaymentRequestPlus::getMerchant(X509_STORE* certStore, QString& merchant) c
             !EVP_VerifyFinal(ctx, (const unsigned char*)paymentRequest.signature().data(), (unsigned int)paymentRequest.signature().size(), pubkey)) {
             throw SSLVerifyError("Bad signature, invalid payment request.");
         }
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#if HAVE_DECL_EVP_MD_CTX_NEW
         EVP_MD_CTX_free(ctx);
 #endif