Refuse "local" lines in pg_hba.conf on platforms that don't support it

This makes the behavior compatible with that of hostssl, which
also throws an error when there is no SSL support included.

src/backend/libpq/hba.c

@@ -824,7 +824,16 @@ parse_hba_line(List *line, int line_num, HbaLine *parsedline)
 	token = lfirst(line_item);
 	if (strcmp(token, "local") == 0)
 	{
+#ifdef HAVE_UNIX_SOCKETS
 		parsedline->conntype = ctLocal;
+#else
+		ereport(LOG,
+				(errcode(ERRCODE_CONFIG_FILE_ERROR),
+				 errmsg("local connections are not supported by this build"),
+				 errcontext("line %d of configuration file \"%s\"",
+							line_num, HbaFileName)));
+		return false;
+#endif
 	}
 	else if (strcmp(token, "host") == 0
 			 || strcmp(token, "hostssl") == 0