buildworld of HEAD failing under 8.1-RELEASE

I am getting the following error when trying to build HEAD on an
8.1-RELEASE build machine (i386 jail on an amd64 host):

===> lib/clang/libllvmanalysis (all)
/usr/d2/users/rstone/git/svos/lib/clang/libllvmanalysis/../../../contrib/llvm/lib/Analysis/ConstantFolding.cpp:
In function 'llvm::Constant* llvm::ConstantFoldCall(llvm::Function*,
llvm::ArrayRef<llvm::Constant*>, const llvm::TargetLibraryInfo*)':
/usr/d2/users/rstone/git/svos/lib/clang/libllvmanalysis/../../../contrib/llvm/lib/Analysis/ConstantFolding.cpp:1310:
error: 'log2' was not declared in this scope
*** [ConstantFolding.o] Error code 1
1 error
*** [all] Error code 2
1 error
*** [cross-tools] Error code 2
1 error
*** [_cross-tools] Error code 2
1 error
*** Error code 2
1 error

Is there anything that I can do other than build on another machine?  I
don't control the build machines at $WORK so I'm not sure whether I can get
them upgraded. :(