Don't specify document_root in embedded_c if NO_FILES

It makes sense to compile the sample with NO_FILES, and in that case it
does not make sense to force the option.

examples/embedded_c/embedded_c.c

@@ -956,8 +956,10 @@ int
 main(int argc, char *argv[])
 {
 	const char *options[] = {
+#if !defined(NO_FILES)
 	    "document_root",
 	    DOCUMENT_ROOT,
+#endif
 	    "listening_ports",
 	    PORT,
 	    "request_timeout_ms",