This patch by Cherry Zhang fixes the Go frontend to not propagate
address-taken of a slice element to the slice.

Array_index_expression may be used for indexing/slicing array or
slice. If a slice element is address taken, the slice itself is not
necessarily address taken. Only propagate address-taken for arrays.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian