gdb/testsuite: add DWARF 5 + split DWARF + type units board

gdb/testsuite: add DWARF 5 + split DWARF + type units board

I'm currently fixing bugs and performance issues when GDB encounters
this particular configuration.  Since split DWARF + type units makes GDB
take some code paths not taken by any other board files, I think it
deserves to be its own board file.  One particularity is that the
produced .dwo files have a .debug_info.dwo section that contains some
ype units, in addition to the compile unit.

Add that board to make-check-all.sh.

Change-Id: I245e6f600055a27e0c31f1a4a9af1f68292fe18c
Approved-By: Tom Tromey <tom@tromey.com>