symbols-in-versions: added new CURLSSLBACKEND_ symbols

Author: bagder

docs/libcurl/symbols-in-versions

@@ -635,17 +635,20 @@ CURLSSH_AUTH_NONE               7.16.1
 CURLSSH_AUTH_PASSWORD           7.16.1
 CURLSSH_AUTH_PUBLICKEY          7.16.1
 CURLSSLBACKEND_AXTLS            7.38.0
+CURLSSLBACKEND_BORINGSSL        7.49.0
 CURLSSLBACKEND_CYASSL           7.34.0
 CURLSSLBACKEND_DARWINSSL        7.34.0
 CURLSSLBACKEND_GNUTLS           7.34.0
 CURLSSLBACKEND_GSKIT            7.34.0
+CURLSSLBACKEND_LIBRESSL         7.49.0
 CURLSSLBACKEND_MBEDTLS          7.46.0
 CURLSSLBACKEND_NONE             7.34.0
 CURLSSLBACKEND_NSS              7.34.0
 CURLSSLBACKEND_OPENSSL          7.34.0
 CURLSSLBACKEND_POLARSSL         7.34.0
 CURLSSLBACKEND_QSOSSL           7.34.0        -           7.38.1
 CURLSSLBACKEND_SCHANNEL         7.34.0
+CURLSSLBACKEND_WOLFSSL          7.49.0
 CURLSSLOPT_ALLOW_BEAST          7.25.0
 CURLSSLOPT_NO_REVOKE            7.44.0
 CURLUSESSL_ALL                  7.17.0