<cxxabi.h> not found by clang-3.5 rc1 with libc++

This seems to be exclusive to the rc1, trunk works, clang-3.4 works, etc

ben:~/development/test$ cat abi.cpp
#include <cxxabi.h>

int main() {}

ben:~/development/test$ clang++-3.4 -stdlib=libc++ abi.cpp
ben:~/development/test$ clang++-3.5 -stdlib=libc++ abi.cpp
abi.cpp:1:10: fatal error: 'cxxabi.h' file not found
#include <cxxabi.h>
1 error generated.

As far as I know, they all use the same libc++ install (also trunk) and built against libc++abi.

/usr/include/c++/v1/cxxabi.h exists and is installed when I install libc++.