Enable passing arguments to the inferior in debugglibc.sh

This patch adds the ability to run debugglibc.sh's inferior program with
arguments specified on the command line. This enables convenient debugging
of non-testcase programs such as iconv/iconv_prog or other dynamically
linked programs. Program arguments may be passed using `--' as a separator.

For example:

  $ ./debugglibc.sh -b iconv -- iconv/iconv_prog -f ASCII -t UTF-8 input.txt