Finalize support of nsim_gdb as a test target for ELF32 tool chain tests

Please review. 

2013-05-23  Anton Kolesov <anton.kolesov@synopsys.com>

    * dejagnu/nsim-extra.exp, dejagnu/baseboards/arc-nsim.exp: Change
    functions where watchdog breakpoints are set from 'abort' and '_exit' to
    'exit' and '_exit_r', use NSIM_HOME environment variable to start nsim_gdb
    instance, use option -reconnect of nsim_gdb, use only a limited range of
    TCP ports for GDB communication.