Gist does not build with VC++ anymore

I've updated my VC++ build env with latest CVS, and it no longer builds
because of changes to GIST:

src\backend\access\gist\gistutil.c(237) : error C2057: expected constant
expression
src\backend\access\gist\gistutil.c(237) : error C2466: cannot allocate
an array of constant size 0
src\backend\access\gist\gistutil.c(237) : error C2133: 'storage' :
unknown size


The problem appears to come from:
#define GEVHDRSZ    (offsetof(GistEntryVector, vector[0]))

Which can't be used in this context.

What would be the proper fix for that?

//Magnus