If we want new secure DLL approach to be adopted, we should make
conversion as simple as possible to explain and implement.
I think that replacing

syscall.NewLazyDLL(...) -> windows.NewLazySystemDLL(...)

is easier than

syscall.NewLazyDLL(...) -> &windows.LazyDLL{Name: ..., System: true}

So I propose we introduce convenience function NewLazySystemDLL.

$GOROOT/src/mksyscall_windows.go changes in the following CL.

Change-Id: If3432aff301c347cb355e4e837834696191b2219
Reviewed-on: https://go-review.googlesource.com/21592Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>