No source file named getopt.c.

Hi:

I want to set a break point on some code in getopt.c, but I just got:

////////////////////////////////////////////
(gdb) b getopt.c:100
No source file named getopt.c.
////////////////////////////////////////////

then, I did this to add the source directory of that code, as:

////////////////////////////////////////////
(gdb) directory /home/dingaaa/test/gdb-7.6/libiberty/
Source directories searched: /home/dingaaa/test/gdb-7.6/libiberty:$cdir:$cwd
////////////////////////////////////////////

but still, I get
////////////////////////////////////////////
(gdb) b getopt.c:100
No source file named getopt.c.
////////////////////////////////////////////

BTW: I've changed Makefiles, with `-g -O0`

What's the problem?
Thanks.