Avoid lazy initialization of class variables assigned with simple values

[waj]

Currently all class variables are lazily initialized even when they are declared with a simple initializer with a literal of a simple type. This prevents that and do a direct initialization of the global variable, quite similar to simple constants.

I'm not so happy with this patch as I do with the result, so I'm open to suggestions about how to write this better.

[asterite]

Looks good!

[asterite]

@waj Maybe we can add a couple of specs for this:

1. A spec that proves that inherited simple class variables are initialized
2. A spec that checks that the "init" stuff doesn't appear for simple class variables. Something like this (but looking for the "init:..." thing we use in LLVM).

What do you think?

[waj]

@asterite I just added a spec for 2. Isn't 1 already covered by this spec?

crystal/spec/compiler/codegen/class_var_spec.cr

Lines 359 to 379 in 4a0ca22

	it "doesn't inherit class var value in subclass" do
	run(%(
	class Foo
	@@var = 1
	def self.var
	@@var
	end
	def self.var=(@@var)
	end
	end
	class Bar < Foo
	end
	Foo.var = 2
	Bar.var
	)).to_i.should eq(1)
	end

[asterite]

@waj You are right, just that spec is good, thanks!