`listAllBlocks` should list blocks on the nonmoving heap

listAllBlocks is a function exported by the RTS that runs a callback on every block, but as far as I can tell it doesn't traverse the blocks on the nonmoving heap. This is causing failures in my ghc-debug branch that adds support for the nonmoving heap: ghc-debug!10 (comment 468161)

I'd be happy to offer an MR. I think all that needs to happen is for this function to loop over the nonmoving segments and other things under the nonmoving heap's purview (eg, some large objects, compact regions, etc).