The calling convention in rustboot needs adjustment

[graydon]

The immediate problem is that 'extra args' (closure, object) come after the main args, and this makes it impossible to pass an interior-mode parametric-type argument. The workaround (terribly lame) is to only pass parametric args by alias or exterior.

Need to move extra-args to a (non-optional) leading argument position or take this opportunity to change the calling convention to use regs for the implicits (out, task, closure/obj). This is tempting. Fastcall is fast for a reason.

[froystig]

Fixed in a sequence of commits ending in 25a38ee.