[gdb/testsuite] Use TERM=ansiw in tuiterm for bsd

[gdb/testsuite] Use TERM=ansiw in tuiterm for bsd

TERM=ansi is different on freebsd and linux.  Consequently, many TUI
test-cases (gdb.tui/*.exp and gdb.python/tui*.exp) fail on freebsd.

One of the problems is that send_gdb "<cmd>\r\n" is needed instead of
send_gdb "<cmd>\n".

This is because gdb_send "layout regs\n" translates to
"layout regs<KEY_DOWN>", which evidently missing the carriage return part.

While we can work around this, there are other problems.  There is no color
support, and the cursor keys fail to scroll the source window.

So I went looking for an alternative to TERM=ansi on freebsd, and came across
TERM=ansiw.  Using this didn't work out of the box, but with the fixes in
this series it now does.

I also briefly looked at TERM=ansis, which is interesting because it's
available on both linux and freebsd, but ansiw is a better choice for now.
I've filed PR33179 to document what I learned, with the aim to eventually
follow up and address two test-case failures with TERM=ansis on linux.

Tested on x86_64-freebsd.