# scl enable devtoolset-1.1 bash
# rpm -q devtoolset-1.1-gdb
devtoolset-1.1-gdb-7.5-20.el5
# gdb /bin/true -q -ex sta -ex 's 999999'
Reading symbols from /bin/true...Reading symbols from /usr/lib/debug/bin/true.debug...done.
done.
Temporary breakpoint 1 at 0x10000c38: file true.c, line 63.
Starting program: /bin/true 

Temporary breakpoint 1, main (argc=1, argv=0xffabf654) at true.c:63
63	  setlocale (LC_ALL, "");
Segmentation fault

When stepping manually:
(gdb) 
__ctype_b_loc () at ../include/ctype.h:34
34	  if (__builtin_expect (*u.tablep == NULL, 0))
(gdb) 
_nl_normalize_codeset (codeset=0xfff6fd2a "UTF-8", name_len=1) at l10nflist.c:341
341		if (isalpha ((unsigned char) codeset[cnt]))
(gdb) 
336	  for (cnt = 0; cnt < name_len; ++cnt)
(gdb) 
341		if (isalpha ((unsigned char) codeset[cnt]))
(gdb) 
336	  for (cnt = 0; cnt < name_len; ++cnt)
(gdb) 
345	  retval = (char *) malloc ((only_digit ? 3 : 0) + len + 1);
(gdb) 
Segmentation fault

With system gdb:

# gdb /bin/true -q -ex sta -ex 's 999999' -ex q
Reading symbols from /bin/true...Reading symbols from /usr/lib/debug/bin/true.debug...done.
done.
Temporary breakpoint 1 at 0x10000c38: file true.c, line 63.
Starting program: /bin/true 

Temporary breakpoint 1, main (argc=1, argv=0xffc2f8d4) at true.c:63
63	  setlocale (LC_ALL, "");

Program exited normally.

Seems this doesn't happen on RHEL6.