Clean up buildfarm failures arising from the seemingly straightforward page

Clean up buildfarm failures arising from the seemingly straightforward page
macros patch :-(.  Results from both baiji and mastodon imply that MSVC
fails to perceive offsetof(PageHeaderData, pd_linp[0]) as a constant
expression in some contexts where offsetof(PageHeaderData, pd_linp) works
fine.  Sloth, thy name is Micro.