cannot build 9.2 from an 11-current host

Hi all,

I've got a build machine that does package builds of net/openafs for 
upstream OpenAFS, and is supposed to build packages for all supported 
FreeBSD versions (and a few unsupported ones, too).  I've recently updated 
to r264039M (the 'M' is reverting PCI ARI bits as discussed in a different 
thread), and now when I go back to build a 9.2 chroot, I find that I 
cannot build world:

[...]
c++ -O2 -pipe 
-I/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/usr.bin/clang/tblgen/../../../contrib/llvm/include 
-I/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/usr.bin/clang/tblgen/../../../contrib/llvm/tools/clang/include 
-I/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/usr.bin/clang/tblgen/../../../contrib/llvm/utils/TableGen 
-I. 
-I/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/usr.bin/clang/tblgen/../../../contrib/llvm/../../lib/clang/include 
-DLLVM_ON_UNIX -DLLVM_ON_FREEBSD -D__STDC_LIMIT_MACROS 
-D__STDC_CONSTANT_MACROS -fno-strict-aliasing 
-DLLVM_DEFAULT_TARGET_TRIPLE=\"x86_64-unknown-freebsd9.2\" 
-DLLVM_HOST_TRIPLE=\"x86_64-unknown-freebsd9.2\" -DDEFAULT_SYSROOT=\"\" 
-I/usr/obj/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/tmp/legacy/usr/include 
-fno-exceptions -fno-rtti -c 
/usr/jail/amd64_fbsd_92/JAILROOT/usr/src/usr.bin/clang/tblgen/../../../contrib/llvm/utils/TableGen/X86RecognizableInstr.cpp
make: don't know how to make /usr/lib/libstdc++.a. Stop
*** [bootstrap-tools] Error code 2

Stop in /usr/jail/amd64_fbsd_92/JAILROOT/usr/src.
*** [_bootstrap-tools] Error code 1

Stop in /usr/jail/amd64_fbsd_92/JAILROOT/usr/src.
*** Error code 1

sys/conf/newvers.sh is at r260647 (9.2-RELEASE-p3), and the source tree 
was generated by performing a svn checkout on a different machine and 
tarring up the tree.  (That would be a checkout of releng/9.2 .)

This is supposed to be a supported operation, right?

-Ben