Backport of commit 1642 on the optimiser branch.  Fix to allocation code for X86/64 in Windows.  Presumably this didn't show up before because this function is normally handled by the code-generator.
Backport of commit 1642 on the optimiser branch.  Fix to allocation code for X86/64 in Windows.  Presumably this didn't show up before because this function is normally handled by the code-generator.

git-svn-id: 98787b36aaefbae4b30fa755be920954cd25e1e4@1662 ae7d391e-3f74-4a2b-a0db-a8776840fd2a

polyml/polyml,polyml/polyml,dcjm/polyml,polyml/polyml,dcjm/polyml,dcjm/polyml,dcjm/polyml,mn200/polyml,mn200/polyml,mn200/polyml,mn200/polyml,polyml/polyml