escape: Avoid allocation of varargs parameter.

escape: Avoid allocation of varargs parameter.

    There was a bug in the escape analysis that would cause
    the slice implicitly created to hold varargs parameters to always
    escape, as well as the appended to slice argument.  The intended
    behavior was that the elements of the appendee and appended to
    slice would escape to the heap.  Alongside of these issues,
    the varargs slice would also have a chance to be initialized to an
    invalid memory location if it were stack-allocated.  This has been
    fixed as well.

    Reviewed-on: https://go-review.googlesource.com/30450

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@240826 138bc75d-0d04-0410-961f-82ee72b054a4