This will come in handy if we want to use the LLVM port with a GNU host
compiler.
As of version 13, libc++ uses `__attribute__((using_if_exists))` to
import global LibC functions into the `std` namespace, which allows some
symbols to be absent. GCC does not support this attribute, so it fails
to build libc++ due to some obscure `wchar.h` functions. This means that
cross-compiling libc++ is not possible; and on-target builds would be
tedious, so we'll be better off using the toolchain's `libstdc++`.
In order to propagate errors that occur during UI setup, we have to move
all that logic out of widget/window subclass constructors. This is a
first attempt at doing that, for GUI::SettingsWindow.
The fixes are:
1. Don't copy PCI::DeviceIdentifier during construction. This is a heavy
structure to copy so we definitely don't want to do that. Instead, use
a const reference to it like what happens in other parts in the Kernel.
2. Declare the constructor as explicit to avoid construction errors.
It appears that we don't have almost no cases of a callers passing
exec promises when they call `pledge()`. To simplify the code a bit we
add a default parameter that will pass nullptr for us to `pledge()`.
In the spirit of the Core::System name space having "modern" facades
for classically C functions / Kernel interfaces, it seems appropriate
that we should take Span's of data instead of raw pointer + length
arguments.
The settings for Terminal are extracted into their own application,
TerminalSettings, which is reachable over the normal Settings menu as
well as the same place in the Terminal menu. The font settings are moved
into these settings as well, which are now split up into the "Terminal"
and "View" tabs. The font settings themselves receive an option to
override the selected font with the system default on the user side.
The live update behavior of all of the terminal settings is retained.
The layout of the new TerminalSettings is based around the other
Settings applications, but pixel-perfectness is missing in some places.
It's a bit fiddly and I'd like to have some better GUI::Label auto-size
behavior, but oh well :^)
Some settings tabs, like the ones on the upcoming terminal settings,
need to know when the cancel button is pressed to clean up things like
temporary live updates. Therefore, the SettingsWindow::Tab now features
a cancel_settings callback which does not need to be implemented.
