gdb/testsuite: add "breakpoint always-inserted" axis in gdb.base/continue-after-abort...

gdb/testsuite: add "breakpoint always-inserted" axis in gdb.base/continue-after-aborted-step-over.exp

The test gdb.base/continue-after-aborted-step-over.exp fails on ROCm GDB
[1] when using the unix board (when debugging a standard x86-64/Linux
program), with:

    (gdb) b *0^M
    Breakpoint 2 at 0x0^M
    Warning:^M
    Cannot insert breakpoint 2.^M
    Cannot access memory at address 0x0^M
    ^M
    (gdb) FAIL: gdb.base/continue-after-aborted-step-over.exp: displaced-stepping=off: b *0

This happens because that build of GDB defaults to "set breakpoint
always-inserted on", for reasons that are unrelevant to explain here.
As soon as the breakpoint is created, GDB tries to insert it and
(expectedly) fails.  This causes more text to be output than what the
pattern expects.

It is actually be relevant to run the test with both "set breakpoint
always-inserted" on and off.  With it on, it mimics what happens when
running in non-stop mode, with other threads running.  This is relevant
for upstream even outside of the ROCm port, so here's a patch for it.

Add this other axis and adjust the "b *0" test to handle the extra
output when it is on.

[1] https://github.com/ROCm-Developer-Tools/ROCgdb

gdb/testsuite/ChangeLog:

	* gdb.base/continue-after-aborted-step-over.exp: Add "breakpoint
	always-inserted" axis.
	(do_test): Add breakpoint_always_inserted parameter.

Change-Id: I95126cae563a0b9a72f4a99627809fc34340cd5e