[win32] add support for variable-length syscall data, optional syscall arguments, and variable output length

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:57:35_

PR 406355

my windows syscall data is missing 3 types of information:
- some structs have variable-length data on the end
e.g., PORT_MESSAGE which I do handle today w/ hardcoded support
- some structs have optional fields that don't need to be defined
- need to add post-syscall write size entries: I put in a handful.
should look at all OUT params whose (requested) size comes from an IN param

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=99_