This happens if you first configure with autotools, and then run
cmake. The problem is that the compiler finds the old src/platform.hpp
before looking for the one generated by CMake. Further, there are a
set of macros that configure passes via the command line, yet CMake
passes via platform.hpp. (HAVE_xxx for pollers, at least.) This means
you can't do a CMake build using the autotools platform.hpp.

Solution: remove any src/platform.hpp when running cmake. This is a
workaround. I'll fix the inconsistent macros separately.