cmd/compile: make ascompatte generate less garbage

[josharian]

@crawshaw noted over email:

ascompatte (a) is called a lot, (b) returns a new []_Node, and (c) that return value almost always replaces the []_Node passed in as parameter lr. Might be due for a rewrite inline modifies a Nodes...

Transferring to an issue so that it doesn't get lost.

[quasilyte]

I think this function is gone now.
Could be the right time to close this issue, maybe?

For the reference, git bisect shows that this function was replaced in 2578ac5.

    Prior to this change, walk was responsible for constructing (most of) the stack for function calls.
    ascompatte gathered variadic arguments into a slice.
    It also rewrote n.List from a list of arguments to a list of assignments to stack slots.
    ascompatte was called multiple times to handle the receiver in a method call.
    reorder1 then introduced temporaries into n.List as needed to avoid smashing the stack.
    adjustargs then made extra stack space for go/defer args as needed.

    his change moves stack construction to the SSA construction phase.
    ascompatte, now called walkParams, does all the work that ascompatte and reorder1 did.