Curl_ossl_version: adapted to detect BoringSSL

This seems to be the way it should work. Right now we can't build with
BoringSSL and try this out properly due to a minor API breakage.

lib/vtls/openssl.c

@@ -2831,10 +2831,14 @@ size_t Curl_ossl_version(char *buffer, size_t size)
     }
 
     return snprintf(buffer, size, "%s/%lx.%lx.%lx%s",
+#ifdef OPENSSL_IS_BORINGSSL
+                    "BoringSSL"
+#else
 #ifdef LIBRESSL_VERSION_NUMBER
                     "LibreSSL"
 #else
                     "OpenSSL"
+#endif
 #endif
                     , (ssleay_value>>28)&0xf,
                     (ssleay_value>>20)&0xff,