libtool-base refusing to even start building on ia64-hp-hpux11.31

[Paul Ackersviller <pda%sdf.org@localhost>]

I'm pretty sure much of pkgsrc worked on this box last year, but now
with 2014q4, after bootstrapping, I'm only getting as far as...

ERROR: This package has set PKG_FAIL_REASON:
ERROR: libtool-base-2.4.2nb9 requires a working dlopen().

A glance at mk/dlopen.buildlink3.mk gives me the idea that twiddling
DL_AUTO_VARS might have some effect, but no such luck.

Any clue as to why pkgsrc thinks there's a problem with my dlopen?
There's no indication anything is even being attempted before the above.