Our internal OSX build machines were hitting race conditions while
building the runtime libraries during a bootstrap build, i.e. building
both libcxx and TSAN in the same build. TSAN includes parts of libcxx
(errno.h, ...) but the CMakeLists.txt didn't declare this dependency.
With this change, our (Tableau's) bootstrapping on OSX works as expected.
Headers like errno.h or stdio.h are provided by libc, not libc++, do you know which libc++ headers are needed by TSan?