Added checks to allow building against LibreSSL

It seems that when OpenSSL 1.1.0 support was added, LibreSSL was broken
due to the way version checking was done. This adds extra checks for
LIBRESSL_VERSION_NUMBER where applicable.

tool/openssl-compat.h

@@ -13,7 +13,7 @@
 #ifndef _WINDOWS
 
 #include <openssl/opensslv.h>
-#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#if (OPENSSL_VERSION_NUMBER < 0x10100000L) || defined(LIBRESSL_VERSION_NUMBER)
 
 #include <openssl/rsa.h>
 #include <openssl/dsa.h>
@@ -33,5 +33,5 @@ void X509_SIG_getm(X509_SIG *sig, X509_ALGOR **palg,
                    ASN1_OCTET_STRING **pdigest);
 
 #endif /* _WINDOWS */
-#endif /* OPENSSL_VERSION_NUMBER */
+#endif /* OPENSSL_VERSION_NUMBER || LIBRESSL_VERSION_NUMBER */
 #endif /* LIBCRYPTO_COMPAT_H */