compiler: fix slice/array evaluation order bug

compiler: fix slice/array evaluation order bug

    There was a phase ordering issue in the handling of "keyed" array
    literal expressions: the lowering phase was canonicalizing the
    indices/vals before the phase that fixed evaluation order, meaning that
    the evaluation order was incorrect. The fix is to capture the orginal
    ordering and use that ordering when doing traversals (there is already
    something similar being done for struct literal expressions).

    Fixes golang/go#17640

    Reviewed-on: https://go-review.googlesource.com/32296

From-SVN: r241688