Problem: cmake fails with #error None of the ZMQ_USE_* macros defined

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.

CMakeLists.txt

@@ -552,6 +552,9 @@ foreach (source ${rc-sources})
   configure_file (${CMAKE_CURRENT_SOURCE_DIR}/src/${source}.in ${CMAKE_CURRENT_BINARY_DIR}/${source})
 endforeach ()
 
+#   Delete any src/platform.hpp left by configure
+file (REMOVE ${CMAKE_CURRENT_SOURCE_DIR}/src/platform.hpp)
+
 configure_file (${CMAKE_CURRENT_SOURCE_DIR}/builds/cmake/platform.hpp.in ${CMAKE_CURRENT_BINARY_DIR}/platform.hpp)
 list (APPEND sources ${CMAKE_CURRENT_BINARY_DIR}/platform.hpp)