runtime: recreate function called by cgo -gccgo

runtime: recreate function called by cgo -gccgo

    When using cgo -gccgo calls to C.GoString, C.GoStringN, and C.GoBytes
    are turned into calls to __go_byte_array_to_string and
    __go_string_to_byte_array.  Those functions were removed when the string
    code was copied from Go 1.7, but we still need them for cgo.  While cgo
    should be updated, old versions will exist for some time.

    Reviewed-on: https://go-review.googlesource.com/32474

From-SVN: r241743