Kernel: Add bare minimum for global constructors

[ADKaster]

Add text.startup to the .text block, add .ctors as well.
Use them in init.cpp to call global constructors after
gtd and idt init. That way any funky constructors should be ok.

Also defines some Itanium C++ ABI methods that probably shouldn't be,
but without them the linker gets very angry.
If the code ever actually tries to use __dso_handle or call
__cxa_atexit, there's bigger problems with the kernel.

Bit of a hack would be an understatement but hey. It works :)

year: 2019, month: 10, day: 31
PIC(i8259): cascading mode, vectors 0x50-0x58
Globalglobalglobalglobalglobal
Global Struct values: 100 10
PS2MouseDevice: Device detected

[awesomekling]

Dude, awesome! :)

[awesomekling]

Let's put an ASSERT_NOT_REACHED(); in this function.

[ADKaster]

done, also removed parameter names

[awesomekling]

I guess you meant to remove this :)

[awesomekling]

I guess you meant to remove this too :)

[ADKaster]

right, had to test somehow

[xTibor]

Typo: somthing -> something

[ADKaster]

spell checker failed me again, fixed

[awesomekling]

Awesome! Thank you for fixing this :)

[bugaevc]

This is cool, but we need to be very conscious about using this, because it will further increase the boot time.

Currently, various global resources are lazily created like this:

serenity/Kernel/Net/UDPSocket.cpp

Lines 15 to 21 in 233ea7e

	Lockable<HashMap<u16, UDPSocket*>>& UDPSocket::sockets_by_port()
	{
	static Lockable<HashMap<u16, UDPSocket*>>* s_map;
	if (!s_map)
	s_map = new Lockable<HashMap<u16, UDPSocket*>>;
	return *s_map;
	}

with global constructors, it could be simplified to just

Lockable<HashMap<u16, UDPSocket*>> g_sockets_by_port; 

at the cost of running the constructor at bootup instead of on first access. Of course we don't have to change existing occurences of this pattern, but it's going to be too tempting to just do this in new code.

I wonder if we could have something like the lazy_static macro to make this both convenient and lazy.