runtime: move schedt type and sched var from C to Go

runtime: move schedt type and sched var from C to Go

    This doesn't change any actual code, it just starts using the Go
    definition of the schedt type and the sched variable rather than the C
    definitions.

    The schedt type is tweaked slightly for gccgo.  We aren't going to
    release goroutine stacks, so we don't need separate gfreeStack and
    gfreeNostack lists.  We only have one size of defer function, so we
    don't need a list of 5 different pools.

    Reviewed-on: https://go-review.googlesource.com/33364

From-SVN: r242600