Compiler intelligence: Pointers to comptime data should not be accessible at runtime

[ghost]

This means, in the ideal case, the following code should not compile:

pub fn testing123() void {
    comptime var value: u32 = 3;
    const pointer = &value;
    var bad = pointer; // this is an undefined address
}

To detect this, we'd either need to make sure that the value of pointer never gets passed to codegen (ideal, hard), or that pointer reads as null in codegen (good enough, easy).

[Vexu]

Should be covered by #1487, #2710 and #3996.

[ghost]

Not quite -- the issue may be the same, but the proposed solution is different.