New board file to run the whole testsuite with a local gdbserver in extended-remote mode

[Joel Brobecker]

>  - many tests that do "attach" assume GDB can figure out what executable
>    the process is running, and load it automatically
>    (target_pid_to_exec_file).  This doesn't work in the remote
>    targets.

I think these testcases should be fixed to avoid tis requirement.
We can always have one specific testcase that test that, and skip
the testcase if testing in extended-remote mode.

> I think this should be good enough to check in as is, and improve as
> follow-ups.

I agree. This is far better than nothing.

-- 
Joel