cmd/compile: fix missing ddd when building call for function instantiation closure

When building a call expression for function instantiation closure, if
it's a variadic function, the CallExpr.IsDDD must be set for typecheck
to work properly. Otherwise, there will be a mismatch between the
arguments type and the function signature.

Fixes #49516

Change-Id: I0af90ee3fcc3e6c8bba8b20e331e044cbce17985
Reviewed-on: https://go-review.googlesource.com/c/go/+/363314


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>