Before, Settings::SetDebugModeEnabled was used; this calls SetBaseOrCurrent() which will usually permanently change the base configuration setting for the debugger to true. Thus, the debugger would remain active even if the --debugger command line option was removed. Now, it remains active only for the current run, like other command-line options.

Note that SetBaseOrCurrent is also used by the "Show Debugging UI" option under Options -> Interface; this means that if the debugger is turned off (or off and then back on) by the user while --debugger is specified, this will be reset to whatever the base configuration had when Dolphin is closed and reopened. This behavior is consistent with the rest of the UI.

To my understanding, the --debugger option is something from 5.0 stable/DolphinWx where there was no way to toggle the debug UI in the settings (and the command-line option was the only way of enabling it). It's less useful nowadays.

Fixes a crash that could occur if the static constructor function for
the MainSettings.cpp TU happened to run before the variables in
Common/Version.cpp are initialised. (This is known as the static
initialisation order fiasco.)

By using wrapper functions, those variables are now guaranteed to be
constructed on first use.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Both structs are already in the Config namespace.

https://bugs.dolphin-emu.org/issues/11888

This also includes another change: DolphinQt will now exit with an
error if you use --batch without specifying a game using any method
(unlike in the past where --batch would be ignored if you didn't
specify a game using --exec, even if you had used --nand-title).
The main reason why I did this was because coding the alternative
(ignoring --batch) would be annoying with render to main involved.