[gdb/testsuite, Tcl 9.0] Avoid non-UTF-8 GDB IO (part 2)

With Tcl 9.0 and test-cases gdb.ada/non-ascii-latin-{1,3}.exp we run into
similar problems as reported in the previous patch.

Work around this by avoiding non-UTF-8 chars in:
- gdb input by using a command file, and
- gdb output by not printing a source line containing such chars

Approved-By: Tom Tromey <tom@tromey.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33948