Cygwin: Use MEMORY_WORKING_SET_EX_INFORMATION in dumper

Cygwin: Use MEMORY_WORKING_SET_EX_INFORMATION in dumper

Use the (undocumented) MEMORY_WORKING_SET_EX_INFORMATION in dumper to
determine if a MEM_IMAGE region is unsharable, and hence has been
modified.

After this, we will end up dumping memory regions where:

- state is MEM_COMMIT (i.e. is not MEM_RESERVE or MEM_FREE), and
-- type is MEM_PRIVATE and protection allows reads (i.e. not a guardpage), or
-- type is MEM_IMAGE and attribute is non-sharable (i.e. it was WC, got
   written to, and is now a RW copy)