I cannot access to a Tru64 workstation.
So I cannot myself test p7zip for this target.
I don't know pkgsrc nor bmake.
I don't know who maintains this pkgsrc package.
As I can this in "===> Patching for p7zip-9.20.1", pkgsrc seems to patch the official p7zip_9.20.1_src_all.tar.bz2.
If you can, try to add a path like this :
In CPP/myWindows/CPP, change
#define E.
2012-01-20 11:12:55 PST in p7zip