gdb/testsuite: update tests looking for "DWARF 2" debug format

gdb/testsuite: update tests looking for "DWARF 2" debug format

Commit ab557072b8ec ("gdb: use actual DWARF version in compunit's
debugformat field") changes the debug format string in "info source" to
show the actual DWARF version, rather than always show "DWARF 2".

However, it failed to consider that some tests checked for the "DWARF 2"
string to see if the test program is compiled with DWARF debug
information.  Since everything is compiled with DWARF 4 or 5 nowadays,
that changed the behavior of those tests.  Notably, it prevent the
tests using skip_inline_var_tests to run.

Grep through the testsuite for "DWARF 2" and change all occurrences I
could find to use "DWARF [0-9]" instead (that string is passed to TCL's
string match).

Change-Id: Ic7fb0217fb9623880c6f155da6becba0f567a885