Build failure on amd64

I've been seeing the following for about a week now in CURRENT:

===> gnu/lib/libstdc++ (depend)
.
.
.
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_alloc.cc:41: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_arm.cc:31: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_aux_runtime.cc:34: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_call.cc:33: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
/usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_call.cc:37:23
: error: unwind-pe.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_catch.cc:31: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_exception.cc:34: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_globals.cc:35: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_personality.cc:33: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
/usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_personality.c
c:41:23: error: unwind-pe.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_term_handler.cc:31: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_terminate.cc:34: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_throw.cc:31: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_type.cc:33: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/eh_unex_handler.cc:30: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/pure.cc:32: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
In file included
from /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/vec.cc:37: /usr/src/gnu/lib/libstdc++/../../../contrib/libstdc++/libsupc++/unwind-cxx.h:41:
20: error: unwind.h: No such file or directory
mkdep: compile failed
*** Error code 1

-- 
Conrad J. Sabatier <conrads_at_cox.net>