allow integer literals to be passed to var args parameters and parameters of type var

[dimenus]

consider the following zig code:

const std = @import("std");
const debug = std.debug;
const MyEnum = enum {
    Zero,
    One,
    Two,
    Three,
};
pub fn main() -> %void {
    debug.warn("{}\n", @sizeOf(MyEnum));
}

fails with:
error: parameter of type '(integer literal)' requires comptime

It would feel much better if 'sizeOf' was defined to either return a u32 or would automatically coerce into the appropriate type rather than having to cast it.

[andrewrk]

More generally, we should allow integer literals to be passed to a parameter of type var. This is planned.

[thejoshwolfe]

How does this work? is the function instantiated for every different literal value?

[andrewrk]

That's correct. Also it still doesn't work with var args because of #557. I'm considering fixing it by replacing var args with a tuple type (see #533). Someone on IRC also suggested that tuple types could be implemented in userland if we had @reflect and @reify (See #383).