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/libltp/lib/dataascii.c

@@ -54,7 +54,7 @@ int offset;
    int ind;	/* index into CHARS array */
    char *chr;
    int chars_size;
-   char *charlist;
+   const char *charlist;
 
 	chr=buffer;
 	total=offset+bsize;
@@ -90,7 +90,7 @@ char **errmsg;
    int ind;	/* index into CHARS array */
    char *chr;
    int chars_size;
-   char *charlist;
+   const char *charlist;
 
 	chr=buffer;
 	total=offset+bsize;