gcc: upgrade 11.2 -> current 12 snapshot

gcc 12 is expected to be released this month or early next month.
Update so we're prepared.
This keeps/ports all patches currently applied to 11.2 that haven't
landed upstream yet.

[v2: Back out the zephyr DWARF-4 workaround]

Signed-off-by: Bernhard Rosenkränzer <bernhard.rosenkraenzer.ext@huawei.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>