runtime: work around escaping closure in export_test.go

runtime: work around escaping closure in export_test.go

    When compiling runtime, it is not allowed for local variables
    and closures to be heap allocated. In one test, there is a go
    statement with a closure. In the gc compiler, it distinguishes
    capturing variable by value vs. by address, and rewrites it to
    passing the captured values as arguments. Currently we don't
    have this, and the escape analysis decides to heap allocate the
    closure and also the captured variables, which is not allowed.
    Work around it by passing the variables explicitly.

    This is in preparation of turning on escape analysis for the
    runtime.

    Reviewed-on: https://go-review.googlesource.com/86245

From-SVN: r256419