Multilibs - how to avoid building the default one twice

[Zack Weinberg]

The ia64-hpux target builds 32- and 64-bit multilibs.  These
correspond to the -milp32 and -mlp64 command line switches, and so
there is

MULTILIB_OPTIONS = milp32/mlp64

in config/ia64/t-hpux.

Now, the default for this target is -milp32 (i.e. if neither option is
specified, that's what you get).  Yet we build separate libraries for
the no-options case.  Is there any way to avoid that?  I tried

MULTILIB_MATCHES = milp32=

but it doesn't have any effect.

zw