Make ssl_check_cert_usage() dependent on POLARSSL_X509_CRT_PARSE_C

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 6e01494..8575181 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4765,6 +4765,7 @@
 }
 #endif
 
+#if defined(POLARSSL_X509_CRT_PARSE_C)
 int ssl_check_cert_usage( const x509_crt *cert,
                           const ssl_ciphersuite_t *ciphersuite,
                           int cert_endpoint )
@@ -4821,3 +4822,4 @@
 
     return( 0 );
 }
+#endif /* POLARSSL_X509_CRT_PARSE_C */