immutable ctors, immutable members, and TDPL

[Dicebot]

Also one issue Don has brought my attention to is this snippet:

// -----------------------------

immutable int x = 1;

void main()
{
	import std.stdio;
	writeln(x);
}

static this()
{
	x = 42;
}
// (does not compile in 2.062 and won't in 2.063)

// ------------------------------

Whatever approach is taken, I think it should be consistent with 
structs/classes in a sense that global variables are module 
members and module constructor is, well, constructor.

But it looks very hard to do because "immutable" is implicitly 
"shared". Ideas?