You can work around that error by causing the pointer to escape.
E.g. someGlobal = &X{}

Note: This is a regression. It doesn't happen with Go 1.4.2

It's probably @rsc 's call if we want to try to tweak this for 1.5, but there was a lot of work done for escape analysis and some lurking bugs plugged. For this particular case (large data with no pointers allocated on stack) it could probably be allowed to pass, but if pointers are in the large data a phase-after-escape-analysis moves such large stack allocations to the heap, potentially leaking stack pointers into the heap. That is my recollection, at least -- we replaced a potential difficult-to-analyze Heisenbug with a compile-time-error with a workaround.

Changing _ = &X{} to _ = new(X) allows it to compile. ie. the below works fine.

package main

type X struct {
    Array [1 << 16]byte
}

func main() {
    _ = new(X)
}

Same as #15733, fixed by d603c27 since go1.7.