Add 'const' qualifiers where needed to avoid compiler warnings.

* libltp/lib/tst_sig.c (tst_sig): Don't attempt to cleanup on
fatal errors.
* libltp/lib/parse_opts.c (parse_opts): Initialize allocated
string to prevent heap corruption.

winsup/testsuite/winsup.api/ltp/alarm02.c

@@ -119,7 +119,7 @@ main(int ac, char **av)
 
     /* Parameters for usc code  */
     int lc;             /* loop counter */
-    char *msg;          /* message returned from parse_opts */
+    const char *msg;          /* message returned from parse_opts */
 
     /* Parameters for alarm test */
     char *buf[] = { "-1", "ULONG_MAX", "ULONG_MAX+1"};